detector. Another good use of this form is for photographers using
film to find the amount of sky that will fit on their film. To cover
this wide range of applications, the measures may be specified in any
of several common units by adding the appropriate suffix. Default
units are shown in parentheses.
The second calculator uses the apparent field of view while looking
into an eyepiece and divides this by the magnification, which in turn
is found from the ratio of focal lengths for the primary mirror and
the eyepiece. Typical eyepieces provide about 45 degrees apparent
fields of view, and some premium ones can go to 60 degrees or more.
After using either method, the resulting sky angle can be assigned to
the Width or Height scale for the next eyepiece by using the Set W and
H buttons to the right.
Saving Eyepiece Definitions
This portion of the Eyepieces window allows you to Add
the current eyepiece settings to a list of favorites. A simple
name is chosen automatically but you may change this to be more
meaningful to you. Each such eyepiece may be Deleted from the set or put to Use by using the buttons on the
left. To the right of each eyepiece is a reminder of its width, height
and a code letter for its shape and size.
The buttons below the table of favorite eyepieces allow you to Save
and later Load the table to a file. These files have the
extension .epd. When saving, the new file is always created in
the Private directory. When
loading, files with this suffix are first checked for in the Private
directory and if
not found in the Shared directory. The suffix is automatically added if
not entered in the file name field. The file named in the Save field is
also the file that is automatically loaded when XEphem starts. This
file name can be saved in the Preferences » Save window in
the Skyview -- Eyepieces section as EyePDefFile.
Saving Sky View Eyepiece Placements
This portion of the Eyepieces window allows you to Save and
later Load the set of eyepieces currently defined on the Sky
View to a file. These files have the extension .epp. When
saving, the new file is always created in
the Private directory. When
loading, files with this suffix are first checked for in the Private
directory and if
not found in the Shared directory. The suffix is automatically added if
not entered in the file name field. The file named in the Save field is
also the file that is automatically loaded when XEphem starts. This
file name can be saved in the Preferences » Save window in
the Skyview -- Eyepieces section as EyePPosFile.
Delete all placed eyepieces
After at least one eyepiece has been placed in the Sky
View, a button
at the bottom of this window will become available to permanently Delete all placed eyepieces
currently anywhere on the Sky View. You may also delete them
individually from the Sky View from the right-click popup or if you
just want to temporarily turn all Eyepieces off and back on later, use
the Eyepieces control in the Control
» Options window.
Close
Across the bottom are buttons to Close
the window and Help to get
more
information. Closing the window has no effect on eyepieces already
placed in the Sky View.
5.5.9 Coordinates
This brings up a simple dialog which
allows you to type in (or copy/paste) and convert among several
common coordinate systems used in astronomy. The coordinates may be
set from or used to repoint the Sky View. See
Coordinate
converter.
5.5.10 User
annotation
This selection brings up a window
which
allows text and lines to be drawn over the image. See
Annotation.
5.6 Sky View Images menu
The Images menu can bring up three windows.
Load and save...
This window controls loading local
FITS
files, downloading them from the Net, and saving them locally.
Analysis tools...
This window provides a variety of
image
analysis and processing tools. Settings made in this window can also
effect what the mouse does in the Sky View when an image is being
displayed.
WCS Solver...
This window provides a means to add
World Coordinate System headers to a FITS file. With WCS, XEphem
(and many other programs) can compute the RA and Dec of each pixel
in the file, not just its X and Y pixel coordinates. This capability
opens the door to many interesting possibilities. The algorithm
performs
a pattern match between the star-like artifacts in the image and the
GSC
and/or USNO star catalogs.
5.6.1 Load and Save FITS
images
This
window allows you to display a FITS file in the Sky View window. You
may display local files or download the Digital Sky Survey directly
from the Internet. The image is resized to match the size of the Sky
View window. Once an image is displayed, all graphical features of the
Sky View are available, such as grids and labeling objects loaded in
the XEphem database. Most of these features require that WCS headers
be present in the image. XEphem can help create these using the WCS Solver tool.
Resizing the window will change the size of the scrolled text
area displaying the FITS header fields.
Open FITS file
Clicking on the option menu will
display a list of all FITS files in the
Private
and Shared directories in a popup menu. All files with the name
extension .fts, .fits, or .fit will be included. Clicking on a file in
the popup list will display it.
Download
This button heads up the section for
downloading Digital Sky Survey images from the Internet You may
choose generations 1 and 2, and either Red or Blue filters for the
latter. The DSS is maintained by the Space Telescope Science
Institute, STScI, in the United States or the European Southern
Observatory, ESO, research facility in Germany. The image data from
either site is identical, so choosing which to use depends only on
availability and whichever is faster for you.
The size and position of the image are that of the current Sky View
settings, but the size is limited to 30 arc minutes by agreement
with each institution. Before attempting a download, use the File » Network setup
window off the Main menubar to configure your Internet connection.
Clicking Display will begin the download. A progress meter will display
remaining time. A Stop window is provided if you care to abandon the
effort. The header of the http server response message is in the
Main File » Syetem Log
window; check there if an error occurs.
FITS Header:
This section consists mainly of a
scrolled text area which shows each field in the FITS header.
If the
header contains any of the fields EPOCH, JD or DATE-OBS then the
date of the observation is displayed above the header. The button
labeled Set time will also
come
alive which allows setting the main XEphem time and date to this
value. This is handy when checking for asteroids, comets or using
the proper motion catalogs with an image. EPOCH must be a decimal year;
JD must be a decimal Julian Date; or DATE-OBS must be either in ISO
8601
format (YYYY-MM-DDTHH:MM:SS), YYYY[/-]MM[/-]DD, or MM[/-]DD[/-]YY
where YY is assumed to be the number of years since 2000 if less than
50 otherwise years since 1900.
In order to be displayed by XEphem, the header in a FITS file must
contain at least the mandatory fields SIMPLE, BITPIX, NAXIS, NAXIS1,
NAXIS2 and END. Only files with BITPIX 8 or 16 and NAXIS 2 are
supported. Both DSS PLATE headers and the traditional World
Coordinate System fields (CTYPE, CROTA, CRPIX, CDELT and CRVAL, 1 and
2) are supported. BSCALE and BZERO are not supported at this time.
Note: XEphem treats the 16
bit pixels as unsigned values from 0 through 65535, unlike the
standard which specifies they be treated as signed with values from
-32768 through 32767. XEphem assigns the coordinate [0,0] to be the
center of the first pixel in the file, unlike the standard which
specifies this position be at coordinate [1,1].
Save as:
The image currently displayed, if any,
may be saved to disk as a FITS file. The file name is specified in
the text field provided. If
Auto
name is turned on, a filename is automatically created derived
from the RA and Dec of the center of the image. An attempt is made to
preserve any existing directory and filename extensions, such that
the filename is constructed between the right-most '/' and the
right-most '.' characters, if possible. You may also type in your
own name.
When an image is saved, its current contrast settings are added to
the FITS headers. If these fields are present when the file is
opened these settings will automatically be put back into effect.
See
Contrast.
File
watch:
This feature allows XEphem to
automatically discover and display FITS files that were created by
another program. When Watch is
turned on, XEphem will try to open the watch
file named in the text field provided here approximately once each
second and display the file named on the first line of the watch file. If successful XEphem
removes the watch file as a
means to handshake the image has been displayed.
With this feature and the popularity of various networked file systems
(NFS, Samba, etc) it is quite reasonable to display images with
XEphem that were captured on an entirely different computer, or on
the same computer running camera control software unrelated to
XEphem.
A further note to implementors: XEphem also supports the watch file being a fifo. In this
case, XEphem will open the fifo and block trying to read a path name up
to the first newline. There is no handshake in this case. The fifo
approach is actually a bit more efficient than the file approach
because no polling is required.
5.6.2 Image Analysis Tools
The Sky Image Tools window offers several functions with which to
analyze the FITS file showing in the Sky View. There are a few sample
FITS files included with which to practice using the tools.
The window is divided into several separate sections, each of which
can be opened and closed as desired. Always present at the top of the
window is a block of basic information about the image. The statistics
ignore a border of 8 pixels. The information shown is: file name;
width and height; value and location of brightest pixel; value of
dimmest pixel; mean, median and standard deviation of all pixels.
Note two important differences
between XEphem and FITS: 1) XEphem treats the 16 bit image pixels as
unsigned values from 0 through 65535, unlike the FITS standard which
specifies they be treated as signed with values from -32768 through
32767. 2) XEphem image coordinates are one less than the FITS
standard. FITS defines the center of the first pixel in the file to be
at [1,1] while XEphem defines it to be at [0,0].
<IP_ADDRESS> Brightness and
Contrast
This
section controls the mapping between image pixels and screen colors.
It does not modify image pixels in any way.
This section may
also
be opened using the button in the left Sky View toolbar that looks like
a circle filled with black on the right half.
The top nine buttons offer shortcuts to set or adjust the image
appearance according to predefined algorithms.
Reverse
toggles between assigning brightness
in
direct or inverse proportion to image pixel values.
Narrow, Wide and Full
correspond to high, medium and low
contrast settings. These are implemented using increasingly broader
assignments of brightness about the mean pixel value in the image.
Narrow assigns full black and white to the mean ± 1/3 Std Dev.
Wide assigns black to mean - 1*StdDev and white to mean + 2*StdDev.
Full
assigns black to the smallest pixel and white to the largest pixel
in the entire image.
Sharper and Duller
change contrast by changing the slope
of the pixel-to-brightness map to be steeper or flatter.
Brighter and Darker
change the brightness by shifting the
center of the pixel-to-brightness map to higher or lower pixel
values.
Nominal
ignores the statistical distribution
of
pixel values and sets the map entirely on the basis of the minimum
and maximum pixel.
Low and Hi
are text fields in which one may type
(or paste) the exact pixel values to be assigned to black and white.
A new value takes effect when Enter is pressed. These fields also
always show the current settings installed by any of the shortcuts.
Gammas
is set using the scale just above the
graph. The mapping from pixels to display colors is a power
function. Values of gamma less than 1 emphasize dark pixels, gamma
values greater than 1 emphasize bright pixels.
The graph contains two
overlaid
plots. The horizontal axis for each plot is the same: the full range
of pixel values within the image, with lowest on the left. The orange line is a histogram of the
number of pixels with each value. The yellow
line indicates the brightness at which each pixel value will be
displayed on the screen. You may control the black and white limits of
the mapping function from the graph by dragging the red arrows at the top of the
diagram.
You may control gamma by sliding the scale ust above the graph.
When XEphem saves an image, it adds three fields to the FITS header
to save the current contrast settings. When it loads an image, if
these fields are present they are used to restore the same display
contrast. If these fields are not present, the Wide setting is used.
These fields are: XELOGLUT: the pixel value assigned to black
XEHIGLUT: the pixel value assigned to white XEGAMMA: the value of
Gamma.
<IP_ADDRESS> Cross section Slice
Opening
this section lets you use the mouse to drag a line across the image
and display the pixels along that line. The graph is labeled
vertically in pixel value, horizontally as pixel distance from the
starting point. The line begins where the left mouse button
is first depressed.
Full pixel range toggle when set scales the vertical
scale to the full range of pixel values in the image, else scales to
the pixel range from Lo to Hi as defined in the
Brightness and Contrast section.
This section may
also
be opened using the button in the right Sky View toolbar that looks
like a slice of bread.
<IP_ADDRESS> Magnifying Glass
This
section gives control over and shows information about the pixels in
the magnifying glass.
Click and hold the left mouse button as you roam over the image and
you will see an expanded view of the pixels. The Size and Magnifying power of the glass can be
set as desired using the two rows of toggle buttons. Note the numbers
on these buttons are in units of screen pixels, not image pixels. So
for example if you zoom in on an area the magnifying glass will expand
it correspondingly further.
While roaming you
might want to turn on the Jump to Max button on the right hand toolbar.
It is the one with the bright dot in the center to which a meandering
arrow finally points. When this button is on, XEphem will begin at the
pixel under the real cursor and walk the gradient to the brightest
connected pixel. All processing proceeds as though this brightest
pixel is where the cursor really pointed.
Statistics about the image pixels under the glass are shown in the
table. All values are in pixels, all locations are in image
coordinates.
Fractional image coordinates occur because the image is resized to fit
the window which results in rational values for the scale factors. If
you zoom in enough to clearly see individual image pixels, you can see
that the coordinate system for image pixels puts the integral position
in the center.
The statistics in the table include:
- Size of the area under the glass;
- Value and location of the center;
- Value and location of the largest pixel under the glass;
- Value of the minimum pixel;
- Mean value of all glass pixels;
- Median value of all glass pixels;
- One Standard Deviation of the pixel values about the mean.
Below the statistics box you can optionally open windows that plot
the row or column through the center of the glass. The horizontal axis
of each graph is in image pixels, the vertical is in image pixel
values.
This section may
also
be opened using the button in the right Sky View toolbar that looks
like a box containing a few stars much larger than the others.
However, since the glass is useful in its own right, the toolbar
button only opens this section if the Image Tools window is already
up. Similarly, closing this section does not also turn off the toolbar
button.
<IP_ADDRESS> Region of Interest
This
section lets you use the mouse to draw a rectangle over the image and
get statistics about the pixels within this region. The area is the
same as that which can be used to specify a region in which to zoom.
This section may also
be opened by the right toolbar button that looks like a boxdrawn around
a galaxy.
The following statistics about the image pixels in the ROI are shown
in the table:
- Length of the diagonal;
- Width and height of the region;
- Value and location of the cursor as you draw the ROI;
- Value and location of the largest pixel in the ROI;
- Value of the minimum pixel;
- Mean value of all ROI pixels;
- Median value of all ROI pixels;
- One Standard Deviation of the pixel values about the mean.
<IP_ADDRESS> 2D Gaussian
Measurements
This
section is based on results of modeling stars with a 2 dimensional
Gaussian.
The model finds the coefficients in the following function of pixel
coordinates x and y that minimizes the Chi square error with each
pixel in an area:
g(x,y)
= B + A*exp(-0.5*(sqr((x-mx)/sx) + sqr((y-my)/sy)))
where
mx is the row coordinate from some
reference position,
my is the same for a column,
sx is the standard deviation of the pixel values along a row,
sy is the same for a column,
A is the peak height of function ( = g(xm,ym) - g(inf,inf)),
B is the mean of the row and column pixels.
[mx,my] is then taken to be the location of the star, the volume as
proportional to A*sx*sy as a measure of its magnitude, and B a measure
of the mean noise level of the surrounding pixels.
In practice, we find this method converges quickly and yields
positional results accurate to .2 pixel or so. Magnitudes and their
error estimates depend strongly on whether the image was ever
compressed, proper image correction, linearity of ADU counts with
brightness, and other factors. When these factors are properly
addressed, magnitude ratios seem to be good to .02 mag or so over
differences of several magnitudes.
The text box shows the results of this fitting process on the image
pixels that are centered on the cursor and lie within the area defined
by the magnifying glass settings (whether or not the glass is actually
turned on). The numbers report the following:
- Relative magnitude difference and error estimate between the
current star and the reference star;
- Position of the star, in image coordinates and in RA/Dec if WCS
header fields are present;
- Full-width-half-max of the star in each dimension in pixels,
and in arc seconds if the image scale is known from header fields
CDELT1 and CDELT2;
- The pixel value representative of the noise level base in the
area (B in the above equation);
- The pixel value of the peak of the Gaussian fit (A+B in the
equation).
If there is a number in the Reference
Mag text field, it is simply added to the magnitude reported.
The idea is to set this to the magnitude of a star (known by
independent means) and use that star as the reference for subsequent
comparison. Since the reference is now calibrated, magnitudes reported
will be absolute not just relative. Except under special situations,
the reference star will not be applicable to other images, although
XEphem does not prevent you from doing this.
The reference star can be established in several ways.
One way is automatic in the sense that
if there is no current reference, the first star that is measured is
also automatically given the role as reference for subsequent
comparisons.
After any star has been measured, it
can be made the reference by clicking on New. Clicking Mark will draw a small circle in
the image around the current reference star in case you lose track
of it.
Another way to set the reference is to
use a catalog star. This is only possible, of course, if the header
includes WCS coordinates. Right-click on the catalog star in the Sky
View and choose the entry New Photom
ref. This will perform the Gaussian fit on the pixels at
that stars location in the image, and assign the Reference Magnitude
to the catalog value.
This section of the
Sky image tools window can be opened by clicking on the button in the
right toolbar that looks like a Gaussian graph (or perhaps a large
nose).
While measuring stars
you might want to turn on the Jump to Max button on the right hand
toolbar too. It is the one with the bright dot in the center to which
a meandering arrow finally points. When this button is on, XEphem will
begin at the pixel under the real cursor and walk the gradient to the
brightest connected pixel. All processing proceeds as though this
brightest pixel is where the cursor really pointed.
5.6.3 Registration
This window lets you register, or align, one or more images to a
reference image. The motivation for this feature is to make a
movie of a moving object that has been captured in several images.
Load the reference image into a new Movie then
load each additional image after it is aligned.
The alignment algorithm requires two stars that appear in each image.
Using two stars is the most general method of defining a 2D coordinate
system and is used for its robust performance. It is possible to use
just one star, but the technique requires the software to make
assumptions about matching features in the image. We feel the slightly
larger burden of defining two stars is worth the results. When choosing
the two reference stars, select stars that are well separated in both
rows
and columns, isolated from neighboring stars, moderately bright and
well
formed.
To begin, load the reference image into Sky View and adjust the
contrast or other visual effects as desired. Then click the first
toggle in the window. The cursor will change over the Sky View to a
small cross. Place the cursor over one reference star and click; you
will see the Gaussian centroid image coordinates of the star
appear in the registration window for Star 1. Now choose a second
reference star and click again. You will see its coordinates appear for
Star 2, the cursor will revert back to the original style and the
toggle button will pop back out. If you ever want to change the
reference image choose different reference stars, you can turn on the
top
toggle again at any time and restart the procedure. This is a good time
to
delete any frames currently in the Movie tool and add the reference
image to form the first frame of a movie.
Now you can load a second image. Again, adjust contrast and so on as
desired. Click on the second toggle in the registration window and
proceed as before to click on the same two stars in the second
image. Be sure to click on the two stars in the same order, so that the
first star clicked when defining the reference stars is also the first
star clicked when working on the second image.
As soon as the second star is clicked on the second image, the image
will be transformed using translation, scaling and rotation in such a
way as to align the two stars with their location in the reference
image. The contrast settings are preserved for you even though the
image
pixel statistics have changed due to the addition of new black pixels
where
the images do not overlap and the loss of pixels that do not fit over
the
reference image. If the results look useful, add it to the Movie.
You may repeat the process of aligning additional images with the
reference image for as many images you like.
Note that while either toggle is turned on in the registration window,
the other image analysis tools are temporarily disabled. Note also that
the algorithm used to transform the image to match the reference image
is
designed primarily for speed. The stars in the transformed image are a
little
distorted and we recommend you not use these images for precise
photometry or
astrometry.
5.6.4 WCS Solver
This window controls a pattern matching
algorithm that attempts to
register the star-like artifacts in a FITS image with the entries in
any or all of the XEphem Field Star catalogs. See Field stars.
The solver will be invoked automatically whenever a FITS file is
loaded whose header includes all the seed fields but does not already
have a WCS solution.
Rows
1-5: setting seed values
The first five rows seed the search
with approximate coordinates for the center of the image, the scale
of the image pixels in each direction, and a possible rotation. The
center must be known to within about one half the smaller of the image
width and height. The scale must be known to within about 10%. The
rotation seed need not be accurate at all, but better estimates will
result in vastly faster solution times. Indeed, better values for any
field will improve the solution speed and also reduce the chances of a
false solution.
Each of the fields may be typed or
pasted into the fields down the left. But often FITS files will
include fields which contain information suitable for this purpose.
In the column down the right you may enter the names of such fields.
Clicking the Use field button
in
a row will read the value from the header field named on the right and
install it into the field on the left of the same row, possibly after
some reformatting and change of units. Certainly not all forms are
supported so please take care to check for proper units and
formatting yourself. The default fields supplied are fairly common
and are known to work if you are lucky enough to have them in your
images.
Row
6: scanning the image for star-like artifacts
The next row contains two parameters
which control the algorithm that scans an image to extract what seem
to be reasonable candidates for stars, that presumably will also be
in a Field star catalog.
Burned
out: This parameter sets the largest pixel value (in the
range 0 .. 65535) a star may contain. Groups of pixels being
considered as a candidate star by the algorithm will immediately
reject the entire group if even one pixel is higher than this. The
idea here is that if a star is so bright as to be even a little burned
out, its centroided position is likely to be worse than not using it
at all. If you feel otherwise, set this to 65535 and no groups will
be rejected (at least for this reason).
S/N
ratio: This parameter sets the minimum signal-to-noise ratio
of a candidate star. The algorithm breaks an image into several
smaller regions and computes several statistics of all the pixels in
that region. In order for a group of pixels to be considered a star,
its
brightest pixel must be at least the median plus this parameter
multiplied by the standard deviation computed from the statistics of
the region in which it is located. Basically, the larger this
number, the more distinct the star must be.
Row
7: Setting realistic search goals
The bottom row contains two parameters
that effect the goal of the search algorithm.
Max pix acc: This parameter
tells the search algorithm not to expect position information for
the star-like artifacts extracted from an image to be any better
than this fraction of a pixel.
Min pix acc: This is the
worst pixel distance acceptable between each image star and its
closest catalog star.
Go
Commences the search for a solution
using the image currently in the Sky View and the parameters in
the various fields above. If a solution is found, each star used
in the solution will be circled and statistics about the quality
of the solution will be presented. The WCS fields that
characterize the solution are written into the FITS header. If you like
the solution, Save the
image and this solution will be saved with the image and searching
will not be needed next time.
Mark stars
Clicking this button will draw a small
circle around each group of pixels in the image the algorithm
considers to be a star. Use this to choose good values for Burned
out and S/N ratio.
WCS Solver Tutorial
The first step is to supply suitable seeds values for the
center of the image, the image scale and any suspected rotation. If the
FITS image header contains fields with these values, enter the names of
the fields in the spaces provided and they will be extracted
automatically when the image is loaded. If the header does not contain
this information, or the units are not correct, then seed values must
be entered manually in the fields provided. Note that the pixel scale
values must have the correct sign since the algorithm automatically
takes into account rotation but not flipping.
The second step is to set the SNR value so that Marking stars finds
most of the brightest and well-formed star-like objects in the image,
without also finding bogus star candidates. Also, if the image was over
exposed so that very bright stars are washed out, eliminate these by
reducing the value for burned out stars.
Once good stars are being marked, the last step is to indicate how
accurately star centroids can be determined and how accurate any
solution is likely to be using the bottom two fields of the form.
Another issue is to use an appropriate field star catalog. More
stars is not necessarily better. For example, the GSC 2.2
goes to mag 18 but also tends to have more bogus entries near very
bright stars. If your image contains a very bright star, take note of
the field stars that are near it; you might do better with the GSC 1.2
than 2.2 catalogs.
After adjusting any field, click Go. If a solution is found, the stars
used in the fit will be marked and statistics about the fit will be
displayed.
This algorithm has proven to be very robust over the years. With a
little practice it can usually be made to work quite well.
5.7 Sky View Favorites
menu
This brings up a menu of the current Favorite objects. Clicking an
entry will place a cross-hair over the object and activate the same
popup menu
that would appear if the object had been right-clicked over the map.
If the object is not
within the field of view the Sky View will be moved so the object is
centered. If Alt-Az mode is currently active and the object is below
the horizon, the view will not be changed and a message will suggest
the mode first be changed to RA-Dec.
Favorites may be managed from the Control » Favorites
window. See Favorites.
5.8 Sky View Telescope
menu
The Telescope menu in Sky View
allows you to connect to and control a telescope and, if using the INDI
protocol, any other instrumentation whatsoever. The control can be
performed via a simple fifo connection, or a much more flexible INDI
interface. For a complete description of the INDI protocol, please
download the reference specification from http://www.clearskyinstitute.com/INDI/INDI.pdf.
Here we only describe the INDI configuration window, the INDI
control panel, testing the INDI system using the sample drivers, and
finally the simple fifo interface.
Regardless of which means is used to send a new position to a
telescope, the menu contains a history list of targets. Clicking on one
of these will send that target again. A button is available to erase
the list at any time.
5.8.1 INDI Test Drivers
Beneath the source directory of XEphem is a directory tools/indi.
This contains several sample INDI drivers that together simulate an
entire observatory. Please read the README and follow the instructions
to build and run the sample drivers. This will allow you to perform a
live test of XEphem's INDI windows to be described next.
5.8.2 INDI Configuration
window
The top row of this window contains two text fields by
which you to
specify the TCP/IP host and port name to which a connection is to be
made to an INDI driver or server. The default values are suitable for
running the test drivers mentioned above.
The remaining rows define the mapping between internal XEphem
functionality and the external INDI devices. All information flows over
the INDI protocol based on Properties. Each property is defined as a
Device, a Property and an array of one or more Elements. The INDI
protocol does not
prescribe the names or the meanings of Properties, it is up to the
client and servers to agree. Recommended practice will evolve as
community participation matures. The sample drivers supplied with
XEphem make some possible choices for properties and names.
The default settings in the Configuration window are the correct
mappings for these sample drivers. The idea is to specify the
Device.Property.Element that corresponds to each purpose. The
Configuration window also allows entering a multiplier and offset that
is applied to the INDI value to compute the value in units used within
XEphem. For example, the units for Mount.EQUATORIAL_COORD.RA are hours
but XEphem
wants this value in radians, hence the multiplier set to 0.2617993.
When connecting to drivers for which the
name mapping is not yet known, one technique for discovering their
Properties is to watch the INDI Control Panel (described next) for each
new Property that is reported when connecting toan INDI server.
One of the options is whether to display a marker at the
telescope position on the Sky View. Below this ia a toggle button to
specify whether the Sky
View will automatically Recenter in order to keep the telescope
Marker in the
field of view. The option applies both to INDI and fifo marker
commands. When Recenter is On, then the telescope Marker is
automatically turned off whenever the Sky View is manually adjusted
(the rationale being that one will most likely not want the Sky View to
bounce back to the telescope position after having been manually
changed).
Note that the sample drivers do not support all XEphem functionality.
For example, the sample drivers do not support being sent a new time
and date. This is included in XEphem in case it is useful someday for
some other driver and to illustrate how XEphem stores dates internally
as a modified Julian date, ie, with an offset of 2415020 removed.
5.8.3 INDI Control Panel
This window shows the realtime operation of an INDI
server. It is
divided into a top and bottom section. The proportion of screen space
used by each half may be controlled using the sash control located
just about the bottom scrolled area.
The top half is a scrolled text area that shows the status messages
arriving from each device. Each message is preceded with a time stamp,
followed by the Device followed by the message text. The Erase
button will permanently remove all messages from the scrolled text.
Clicking on the Trace to button will append the current set of
messages to the file named in the text field to the right and append
all further messages to this file until tracing is turned off.
The bottom half shows each INDI Device, Property and Element to which
XEphem is connected. Each Device may be expanded or collapsed to
control screen space. The entire list can be scrolled up and down. The Connect
button controls whether XEphem will connect to the INDI device whose
host and port are defined in the INDI Configuration window. If a
connection is successful, each of the reported Properties will appear
in the bottom scrolled area.
Under each Device is a list of its Properties. Each INDI Property may
be in one of four states: Idle, Ok, Busy and Alert. These are shown as
a light to the left of the Property colored gray, green, yellow and
red, respectively. To the left of each Device is also a light, colored
the same the highest activity color of any of its Properties. In this
way the status of the most active Property can be determined even when
a Device is collapsed in the window.
INDI Properties can be one of four types. These are Numeric, Text,
Switches and Lights. The first three may be read-write or read-only. A
light is always considered read-only (set only by the Device, not by
the operator). Each Element of each Property is shown on one line. The
left side of the line is the label. Following the label is the current
value and, if read-write, followed by a text field for entering a new
value. Read-write Properties will have a push button to the left of
their name to set a new value; pressing Return in the text field will
also set a new value. Switches will show each switch with their label.
Switches may be defined to operate according to the rules one-of-many,
any-of-many and at-most-one.
5.8.4 FIFO Control
Completely separate from the INDI interface, Sky View implements two
simple
fifos for communicating with a telescope control dæmon or other
processes or scripts. Each fifo must be in either the
Private
or
Shared
directory.
- Inbound: A marker may be placed on the Sky View by
writing a text string to the fifo named fifos/xephem_in_fifo.
The format allows for sending either equatorial or horizon coordinates.
To send an equatorial coordinate, the format is "RA:X Dec:Y",
where X
and Y are in radians at epoch 2000.0. To send a horizon coordinate, the
format
is "Alt:X Az:Y", where X and Y are in radians. The Sky View
center pointing position will be changed if necessary to make the
marker
visible. XEphem attempts to open this fifo each time the Sky View
window is
opened and closes it when the view is closed.
- Outbound: If a process has the fifo named fifos/xephem_loc_fifo
open for reading when the Sky View popup menu is activated, then the
menu will
offer a button to send the cursor position to this fifo. The format is
the
same as a line in .edb format. If it is not already open XEphem
attempts to
open this fifo each time the popup is activated, and leaves it open
until
writing to it fails. Each position sent to the fifo is added to the
Telescope history list.
5.9 Sky View History menu
This is the Sky View History control window. All Sky View Options,
Filter settings and pointing values may be saved in a History entry to
make it easy to configure the same way again at a later time. The Edit
pushbutton in the History pulldown menu brings up this window. The
additional pushbuttons in the History pulldown menu correspond to each
defined History entry and make it easy to apply any one history entry
without opening the History control window.
The control window shows the current set of History entries, one per
line. The left portion of each line contains several controls,
described below. The center portion summarizes the entry, showing the
display mode, coordinate system, center position and field of view. The
right portion provides a text field to give the entry a name. This is
the name which appears in the History pulldown menu.
The controls for each History entry are as follows:
Apply
puts the entry into effect, in the
same way as choosing it from the pulldown menu.
Up
Down
moves the entry up or down in the list.
Delete
removes the given entry.
Replace
replaces the entry with the current
Sky View settings.
The buttons across the bottom allow for
additional control of the History list as a whole:
Add
captures the current Sky View
settings
and creates a new History entry. A default name will be created but
you should probably change it to something more descriptive if you
plan to Save the list.
Save
writes all of the current History
entries to a file. The file name is
xephem_skyhist
and will be created in the
Private
directory. You really don't want to know the format of this file.
Load
reads an existing file of History
entries that has been previously Saved and makes them the current
set.
5.10 Sky View Binary Star Map
This window displays a map of a
binary
star system and a matching ephemeris. It is displayed from the popup
that appears when the mouse is right-clicked over a binary object in
the Sky View.
The map is at left, oriented with equatorial N up and E left, as on the
unaided sky. Each star is drawn in a color according to its spectral
class. The primary star is drawn at the center. A scale at the bottom
shows the sky dimensions of the plot.
If complete orbital elements are available, one orbit is plotted at
equal time intervals marked by small dots. The largest dot in the orbit
marks the position of the secondary nearest to the current XEphem time,
medium size dots mark other locations each ten steps.
If only discrete positions for the secondary are known, the plot is
simply one dot for each.
The table on the right lists the position of each plotted secondary
position. The columns are the dot number, year, separation in arc
seconds and
position
angle as degrees East of North. The separation and position angle at
the current XEphem time are available in the More info pull-right menu in the Sky
View popup.
The Print button will print the map and the list.
6.0 Tools menu
The tools menu provides access to a variety of functions.
6.1 Plot values
This window controls the plot generation and display
functionality of XEphem. You may select most numeric information
displayed throughout XEphem, in pairs, to form x/y coordinates of a
plot. You may select up to 40 such pairs. You then specify a file in
which to write the plot information. XEphem adds one line of
information
to the file for each x/y pair each Update iteration step. XEphem can
then plot any such file on the screen.
Selecting data to plot
Click the toggle labeled Select fields to plot to make each
field in the other windows that are eligible for plotting appear as
a pushbutton. Select each such button as desired to form the x or y
component of a plot. As you make the selections, they are listed in
the table. Use the Undo button
to make changes. You may also associate a tag with each line, up to 8
characters in length. These tags will be included in the plot display
for identification later. Once all the field choices have been made you
may return all the windows to their normal operational appearance by
deselecting the same toggle button.
Saving
and restoring a plot configuration
To save this configuration so it can
be
loaded later, specify a file name and click
Save config file. It will be saved
in the
Private directory. The plot
entries will be savde in addition to the plot title field. The
extension for plot configuration files must be
.ptc and will be added automatically
if left off. A configuration file may be
loaded by selecting it from the option popup menu to the right of
Load config file. The menu will list
all files that reside in the Shared and Private directories with
extension .ptc. Note that reloading a configuration only recreates the
Plot's tag, x and y description; to be useful, the fields to which the
reloaded configuration refers must be made active independently.
Specifying the plot file name and title
Type the name of the file to be used
to
contain the plot information in the text field provided. The
extension must be
.plt and
will be added automatically if left off. When
XEphem first needs to write to the file, it will first check for the
existence of the file and, if it already exists and the
Confirmations
Preferences is On,
ask
whether you wish to append to the file or overwrite it.
Enter a short
title for the plot information in
the
text field provided. When XEphem first writes to a plot file, it
will place the contents of the title text field, if it is not empty,
into the file as a comment. All lines within a plot file that do not
begin with an alphanumeric character are considered comments and are
ignored. If the first line of a file is a comment, XEphem will use
it as the title when it displays the plot.
Generating the plot entries
Once the fields have been specified
and
the plot file named and titled, you may select the
Create plot file toggle button when
ready. Now each time XEphem goes through one Update iteration the
values
you have selected and their tags will be written to the plot file.
Note that when plotting is activated, XEphem does not update the
screen until the N Steps count in the Main window
looping section goes to 1. This greatly
speeds the creation of plot files by avoiding screen updates. If you
wish to watch each iteration, set N Steps to 1 and click the Update
button manually for each iteration.
Once all the desired data has been entered into the plot file, toggle
the plot button back off to flush all data and close the file. The
windows that contain each of the fields used in the plot need not be
visible while the plot is being generated. However, each field must
be active, for example its row and column must be selected if they
are in the Data table.
Viewing plot files
Existing plot files may be viewed by
choosing it in the menu to the right of Show
plot file. The menu will list all files that reside in the
Shared and Private directories with extension .plt. As many different
plot files may be viewed simultaneously as desired. Each plot has
separate controls for flipping the X and Y axes and for turning on
and off a reference coordinate grid. The position under the cursor is
displayed above the top of the plot. The XEphem distribution kit
includes a sample plot file of the analemma.
6.2 List values
This window controls the
list generation functionality of XEphem. The fields you select define
columns of a table written to a file as XEphem runs. The text in
these columns looks exactly like their corresponding fields on the
XEphem windows and so are more familiar and readable than the entries
in plot files. They are designed to be used in
further text processing operations or printed as-is. Two spaces are
placed between each column.
Selecting data to list
Select the Select fields toggle button to
make each field in the other windows that are eligible for listing
appear as a pushbutton. Select each such button as desired to define
each column of the listing. As you make the selections, they are
listed in the table here. Use the Undo
bottom to make changes. Once all the column choices have been made
return all the windows to their normal operational appearance by
deselecting the same toggle button.
Saving and restoring a plot configuration
To save this configuration so it can
be
loaded later, specify a file name and click
Save config file. It will be saved
in the
Private
directory. The name of each list item will be saved in addition to the
column and latex options and title field. The extension for list
configuration files must be
.lsc
and will be added automatically if left off.
A configuration file may be loaded by selecting it from the option
popup menu to the right of
Load
config file. The menu will list all files that reside in the
Shared and Private directories with extension .lsc. Note that reloading
a configuration only recreates the Listing fields; to be useful, the
fields to which the reloaded configuration refers must be made active
independently.
Specifying the listing file name and
format
Type the name of the file to be used to
contain the listing in the text field provided. When XEphem first
needs to write to the file, it will first check for the existence of
the file and, if it exists, ask whether you wish to append to the
file or overwrite it.
Choose to print the file in LaTeX
table format by pressing the given button before beginning to list to
the file.
When column headings are
turned
on, they are written to the output file each time the file is
opened.
All lines within a listing file that
do
not begin with an alphanumeric character are considered comments and
are ignored. When XEphem first writes to a listing file, it will
place the contents of the title
text area, if it is not empty, into the file as a comment for your
convenience.
Generating the listing entries
Once the fields have been specified
and
the listing file named and titled, if desired, select the
Create list file toggle button. Now
each time XEphem goes through one iteration the values you have
selected
will be written to the file. Note that when listing is activated,
XEphem
does not update the screen until the N Steps count in the Main window
looping section goes to 1. This greatly
speeds
the creation of plot files by avoiding screen updates. If you wish
to watch each iteration, set N Steps to 1 and click the Update
button manually for each iteration.
Once all the desired data have been entered into the listing file,
toggle the list button back off to flush all data and close the
file. The windows that contain each of the fields used in the
listing need not be visible while the list is being generated.
However, each field must be active, for example its row and column
must be selected if they are in the Data table.
6.3 Solve equation
This
window controls the automatic equation solving facility. You define an
arithmetic or boolean function, using most of the fields XEphem
displays, then XEphem will automatically evaluate the function and
adjust the time on each iteration to solve for the goal. To set up a
function to solve, follow these steps: Enter a function, Compile it,
Select a goal, Set the desired accuracy, Enable solving, Start the
solving process. Each of these steps is described below.
Entering the function
The function may be any arithmetic
expression, in C-language syntax. All of C's comparison, logical and
arithmetic operators are supported as well as several common
arithmetic functions. The complete list is:
+ - * /
&& || > >= == != < <= abs floor sin cos tan asin
acos atan degrad raddeg pi log log10 exp sqrt pow atan2
The function is entered into the text line provided. It may utilize
most of the fields from the other XEphem windows. Press the Enable field buttons button to
make each available field a button. Where ever a field is desired in
the function, position the text insertion cursor at the desired
position and select the field; its name will be inserted into the
function text. When you are finished defining the function, turn off
the field button appearance by selecting the Enable button again.
Compiling the function
Once the function has been created as
desired, it must be compiled by selecting the Compile button (or by pressing the
Enter key on your keyboard). If there are any errors, a diagnostic
message will appear just below the function. Once a function has
been successfully compiled, the message will read No compile errors.
If the function is modified, a message will remind you that it has
not been compiled. Each time a function is successfully compiled,
XEphem updates all fields and evaluates the function. As explained
below, this can be used as an astronomical calculator even when not
actually solving anything.
Selecting a goal
You may choose from any of four
evaluation algorithms, as selected by the trio of radio buttons.
Find Maximum and
Find Minimum
will solve for a maxima
or minima of the function, respectively.
Find 0
will solve for a time when the function evaluates to zero.
Binary will keep incrementing time
by
Step until the state of the function
changes, then do a binary search to find the exact time when the
function changes state. Binary search interprets a function that
evaluates to zero to be in one state and all other values to be the
opposite state. Generally, binary functions are comprised of logical
operators at their outermost expression levels.
Specifying the desired accuracy
Searching will automatically stop when
the time changes by less than the desired accuracy value. Note that
this method of detecting convergence is not based on the value of
the search function itself.
Enabling the solver
Once the function is defined and it
compiles without errors, you may enable searching for a solution by
selecting the button at the top labeled
Solving is Active. Then,
referring now to the
looping section of
the
Main window, each time an Update occurs the solution advances by one
time step until either N Steps iterations have occurred or until
Step becomes less than Accuracy. The initial time and step size are set
from the Main window, and are adjusted automatically as the solution
proceeds. Note that by setting N Steps to 1 and repeatedly selecting
Update you can effectively single-step the process. Solving will
automatically turn off when convergence is detected, the function is
edited or you may turn it off manually at any time by clicking
Solver is Active back off.
Saving
and restoring a solver configuration
To save the Function, Goal and
Accuracy
so it can be loaded later, specify a file name and click
Save to. It will be saved in the
Private directory. The extension for
solver configuration files must be
.svc
and will be added automatically if left off.
A configuration file may be loaded by selecting it from the option
popup menu to the right of
Load file.
The menu will list all files that reside in the Shared and Private
directories with extension .svc. Note that reloading a solver
configuration only recreates the solving conditions; to be useful, the
fields to which the reloaded Function refers must be made active
independently.
Additional notes on using the
equation solver:
When selecting fields for plotting or listing a button appears labeled Use for plotting. You may select
this button to use the evaluated function as an item in the plot or
listing feature. Note that the function may be used in plotting or
listing whether or not actual solving is turned on.
The windows which contain the fields used in the function being
solved need not be visible while solving is in progress. However, the
field must be active, for example their row and column must be
selected if they are in the Data table.
The Close button removes
the Solving window from the screen; it does not effect actual solver
operation in any way.
A successfully compiled function is evaluated each time XEphem
updates. Whenever the function is compiled it is also evaluated using
freshly updated values. In this way, the Solve window can actually be
used as an arbitrary astronomical calculator at any time, whether or
not solving is actually active.
Solving periodic functions can lead to solutions far from the
intended range. You will get best results if you can start the search
near the expected answer and with a modest step size that will reach
the the
nominal solution within a few steps. You can use the plotting
feature to
study
a function and get an idea of the solution, then use the solver
feature to zero in.
Each plot file may be added to a movie loop or
overlayed with text or graphical annotation
using the menu items in the Control menu of each plot.
6.4 Find close pairs
This
window allows you to scan the list of objects currently in memory
brighter than a given magnitude for all pairs which are separated by
less than a given angular distance. Separations will be topocentric or
geocentric depending on the Equatorial Preference
in the Main menubar. The scan does not include field
stars.
These are the essential steps:
- Set the desired maximum separation, in degrees, and faintest
magnitude.
- Set other options via the Options menu, described below.
- Start the scan via the Run button in the Control menu.
- When the scan completes, all pairs meeting the criteria will
appear in the scrolled list.
The columns in the list are:
- Object 1 Magnitude
- Object 1 Name
- Object 2 Magnitude
- Object 2 Name
- Separation, in Degrees:Minutes:Seconds
The entries are sorted in increasing order of separation. The total
number of pairs found and current conditions are reported above the
list and the time when the scan was performed is indicated in the time
stamp label below the list.
6.4.1 Close Pairs Control
menu
Run
This performs one scan. The XEphem
cursor will change to the Watch shape until the scan is complete at
which time the results appear in the scrolled list.
Sky Point
This will place a cross-hair over the
first object of the selected pair on the
Sky View,
re-aiming if it is currently not in the field. Either select the
pair in the list then press this button, or double-click on the
pair in the list. (These commands do nothing if the Sky View is not
currently up.)
List to file...
This selection allows writing the
current list to a file. A window is presented which allows you to enter
a file name. The file is written when you click Ok.
The format of the file begins with a header line that captures the
conditions in effect when the set of close objects was built.
Following the header, there is one line per pair with exactly the
same information as appears in the window list.
Close
This closes the Close Pairs window.
Note that the Auto run option
is
disabled when the window is closed.
6.4.2 Close Pairs Options
menu
Auto run
When this option is active, a scan for
close objects is performed automatically each time an Update is
commanded from the Main window. The prior list is discarded each
time. The scans are not performed if the Close Pairs window is closed.
Auto list
When this option is active, the
results
of each scan are automatically appended to the file last specified
in the List to file window.
This
works whether the scan was performed explicitly via the Control » Run command
here
or implicitly via an Update from the Main window and the Auto run option is active.
Omit fixed pairs
When this option is active, pairs of
Fixed objects are not listed.
Omit planet's own moons
When this option is active, pairs for
which both objects are part of the same planetary system are not listed.
6.4.3 Close Pairs Algorithm
The sky dome is broken into bands of
constant Dec with height equal to the given separation. The database
is scanned once and each object brighter than the given limit is
dealt into its band and the one adjacent in the direction of the
North pole. Each band is then sorted by RA. Each band is then
scanned for close pairs, with rapid cutoff detection due to the
sort. The final list is then sorted by separation, and displayed.
Total time is strongly influenced by the number of pairs in the result.
So when using wide separations it helps to use relatively bright
limiting magnitudes.
6.5 Night at a Glance
This
window displays a 24 hour period with local midnight in the center.
Across the bottom is a scale marking local dates and time and UTC time,
at each even hour. The current XEphem time is marked with a thin
vertical line.
The background gray shading shows when the Sun is up, down and periods
of twilight. The twilight period matches the Sun Dip setting in the
Main window Night section.
Overlayed on the gray background is one horizontal line for each Favorite. The lines show when the object is
above the horizon, the altitude of which is defined in the View » Data Table »
Control » Setup horizon parameter. The lines on the
diagram
pack closer together as the number of objects to display increases; if
things get too crowded try turning off some of the Favorites.
NAAG Control menu
NAAG mouse
Right-clicking near an object's line will pop up a menu
containing its rise, transit and set data. This information is
with respect to the day in which the click occurred.
If the mouse is clicked far from any object, then just the time at that
horizontal position is presented.
The menu always includes a button showing the exact moment
corresponding to the mouse click position. Clicking the button sets the
main XEphem time to this moment.
An interesting exercise is to set up a time loop with a Step size of
a few days and watch how the rise and set times of objects and the
amount and timing of night time are effected throughout the year.
6.6 Coordinate converter
This window performs simple conversions
among several common astronomical coordinate systems. Simply edit (or
paste) any coordinate and the others will update immediately. All
fields are in units of Degrees except RA is in Hours. Fields may be
entered in either sexagesimal or decimal format. For example, either
10:30:00 or 10.5.
Altitude and Azimuth are with respect to the time and location set in
the Main window. These will change to correspond to the RA and Dec
values if an Update is performed.
The top row are astrometric RA and Dec precessed to the given equinox
year, or enter EOD for apparent coordinates at the current epoch.
Unlike the other fields, edits to the equinox field only take effect
on Enter.
The next row are RA and Dec using whatever is set in the Main Window.
The controls across the bottom perform as follows
Close
Closes this window
Sky Point
Centers the Sky View at the current coordinates.
Eyepiece
Places an eyepiece in the Sky View at the coordinates
shown. The Sky View is not recentered. In order to be drawn the Sky
View
Eyepieces Option must be turned on.
Get Sky
Loads each field from the current center position of the
Sky View.
Canonize
Reformats each field in a consistent manner for easier
viewing.
6.7 Observers
logbook
This
tool lets you store observing circumstances and notes. It is typically
used when making observations at the
telescope.
When this window is open, the popup you get when right-clicking on an
object in the Sky View will contain a selection Add to logbook. Clicking on this
choice will automatically fill in the top section of fields in the
logbook pertaining to
observing
circumstances and object information. To these fields you may add your
own Notes in the scrolled text
area at
the bottom, and equipment or User
defined fields if desired.
There are two interesting controls available across the bottom as
follows:
List
This brings up a scrolled list showing
all entries in the logbook whose fields match those selected in the
S
column. The field may contain
glob patterns
for a textual match or be
preceded with < or > for a numerical range match. Only those
fields selected with the
L column will be
shown, and they may be sorted by the field selected in the
K
column.
You may
Save the resulting scrolled list to a text file using
the
file name field provided. Right-clicking on an entry in the scrolled
list will mark the location of that log entry in the Sky View based on
its RA2000 and Dec2000 field values.
Add
This will add the current record to
the
logbook file. In keeping with the convention that log books are written
in ink, there is no mechanism provided for editing or removing existing
entries. Of course, one may always edit the log file independently.
File format
The Observers logbook is a text file in XML format. The format should
be pretty self-explanatory. The file name is xelogbook.xml in the Private
directory. The entire logbook is
contained in one XML element tagged xelogbook
with a version attribute 1.1.
Each log entry is in an element tagged logentry.
Within each logentry is
one element named the same as the label in the window, sans spaces if
any. The date fields are stored in the user's preferred format.
6.8 Movie
loop
The Movie tool allows you to capture any
number of View, Night at a Glance or Plot windows and collect them into a movie. The
frames of the movie can be viewed one at a time or you can set the rate
to change from one frame to next automatically. There are many uses for
this type of function. For example, you could make small changes in
time and make a series showing the movement of an asteroid through the
solar system. Or use it to quickly blink between two FITS images, one
with and one without a potentially new supernova. You might find the Image Registration feature useful to make these
images.
The Control menu has entries to Delete current frame or
Delete all frames of the movie. You may also Save the
frames to individual PNG files. You must specify a prefix then each
file name will be of the format prefixnnn.png where nnn will be
a sequence number starting with 000. The files will be located in the Private directory. XEphem does not save
the frames directly as an actual movie because there are many such
formats and other tools available to collect the files into a movie in
your preferred format. For example, you could convert the PNG files
into GIF files using pngtopnm and ppmtogif tools
from the netpbm
toolkit then make an
animated gif using whirlgif
or gifsicle.
Another possibility is to use convert which is part of the
ImageMagick
collection. Check your system before looking too far, these tools are
often
already installed on many UN*X systems.
Sliding the Frame selection scale will display the indicated
frame. Step +1 and -1 will advance or back up by one
frame. Frames may also be changed automatically by sliding the Frames
per second scale to the desired rate. Changing the displayed frame
manually by any means will automatically reset the frame rate back to
zero. When moving through the frames automatically and encountering the
last frame in the series, the sequence can either reverse and show each
frame back towards the first or jump back to the first and move
forwards again, depending on the Bounce toggle button.
Each window whose contents may be added to a Movie will have an entry
somewhere in its menu bar named "Add to movie". All such windows also
support a short cut of typing Control-m to add the window to the Movie,
so long as the cursor focus is located within the desired window.
7.0 Data menu
The Data menu offers several means to load, search and update the
files XEphem uses for storing objects.
7.1 Files
This
window allows you to load and delete database files to and from memory.
These objects form what is referred to as the XEphem database. These do
not
include the field stars.
Click the Files menu to scan the Private
and Shared directories and pop up a list of all .edb and .tle files
found therein. Click on a file to load it into XEphem memory.
The top section of the window displays a count of each major type of
object and the total number in the database. The counts include Favorites that are not also in the database.
The bottom section lists the catalogs which are currently loaded and
the number of new objects they contributed to memory. Buttons to the
left of each catalog allow the catalog to be Deleted from memory and to display
the Header of the catalog.
The current list of loaded catalogs may be saved so it becomes the
ones automatically loaded when XEphem starts. To do so, go to Preferences » Save and Save the XEphem.DBInitialFiles resource under the
Data Base category.
7.1.1 Files Control menu
Index...
This is a handy shortcut to open the object
index.
Delete all
This deletes all loaded data. The files on disk are not
effected.
Reload all
This reloads all catalogs currently loaded. This is handy
when catalogs have been updated on disk, perhaps by some by some
automatic means.
Open DB Fifo
Listen for database objects arriving via a fifo from
another process. XEphem attempts to reopen the fifo each time the
button
is pressed. The file name of this fifo is "fifos/xephem_db_fifo" in either the
Private or Shared directory. All relevant displays are automatically updated
when data arrives via this fifo. The format of the fifo data is
exactly the same as for any XEphem database file. Due to the way the
fifo data is read and processed, it is important that each line be
terminated with a newline; incomplete last lines can result in loss
of information.
Make Favorite when read 1
If this toggle is on then when a new database file is
loaded and it defines exactly one object, it will also be assigned to
the list of Favorites. This feature also
applies for files loaded when XEphem first starts.
Check alternate names
This toggle turns on or off support for XEphem 3.6's new
support for alternate names. It is motivated entirely by performance.
Recording alternate names and checking for duplicates is quite
expensive and
if not needed can speed up loading and deleting catalogs significantly.
If this toggle is On then when a new database
catalog is loaded each entry's alternate names, if any, will be checked
for
already being loaded and not loaded if found, and new alternates will
be
stored for display and subsequent checking. If this toggle is Off, only
the
first name of each entry is stored and no duplicate names are checked.
Note that even when this option is Off, deleting a catalog still
requires
XEphem to remove all alternate names that might have been recorded when
the
catalog was loaded, so the full performance advantage is only achieved
if this
option was off when each catalog is loaded.
Close
Closes the Data Base window.
7.1.2 File format
This section describes the format of an XEphem database file. The
file name extension is .edb. See the next section for files containing
two-line Earth satellite elements.
<IP_ADDRESS> General format
rules
- Each object occupies one line in the file.
- The order of objects in a file does not matter.
- Lines beginning with anything other than a-z, A-Z or 0-9 are
ignored and may be used for comments.
- Lines are separated into Fields using commas (,).
- Fields may be further subdivided into Subfields with vertical
bars (|).
- All date fields may be in either of two forms:
- month/day/year, where day may contain a fractional portion.
examples: 1/1/1993 and 1/1.234/1993 . Note the format of dates in
database files is always M/D/Y, regardless of the current XEphem
Date format Preference setting; or
- the year as real number as indicated by the presence of a
decimal point, such as 1993.123.
<IP_ADDRESS> Format Details
The first two fields are required and
are always Name and Type. Remaining fields depend on Type.
Field 1
|
One or more object names, each
separated by the Subfield separator, |. Any number of characters may be
present in the file but XEphem only uses the first 20 characters of
each name and only the first 20 names.
|
| Field 2 |
Type designation. Consists of a
single letter designation from the following set (case is significant):
f
|
fixed (or at most exhibits
constant curvilinear proper motion) |
e
|
heliocentric elliptical
orbit |
h
|
heliocentric hyperbolic
orbit |
p
|
heliocentric parabolic
orbit |
E
|
geocentric elliptical
orbit, i.e., Earth satellite |
P
|
built-in planet or natural
satellite name |
|
If
Field 2 is
f the object is fixed and
the
following fields and subfields are defined:
|
SubField 2A |
An optional SubField 2A can be
added to further define an object class code, consisting of
one character from the following list:
A
|
Cluster of galaxies |
B
|
Star, binary. Deprecated
as of version 3.6, gets turned into D internally. Use Field 2
type B if more than one position angle and separation or
orbital elements are
known.
|
C
|
Cluster, globular |
D
|
Star, visual double |
F
|
Nebula, diffuse |
G
|
Galaxy, spiral |
H
|
Galaxy, spherical |
J
|
Radio |
K
|
Nebula, dark |
L
|
Pulsar |
M
|
Star, multiple |
N
|
Nebula, bright |
O
|
Cluster, open |
P
|
Nebula, planetary |
Q
|
Quasar |
R
|
Supernova remnant |
S
|
Star |
T
|
Stellar object |
U
|
Cluster, with nebulosity |
Y
|
Supernova
|
V
|
Star, variable |
|
|
SubField 2B |
If SubField 2A is one of T, B,
D, S or V, optional SubField 2B may consist of up to two spectral
designation characters, typically one letter followed by one numerical
subclass designator. Two examples are O and G3. |
|
|
If SubField 2A is any other
class code, optional SubField 2B may consist of up to two additional
characters to further describe the type.
|
| Field 3 |
Astrometric RA
position coordinate in equinox given by Field 6 always at epoch 2000, given as H:M:S. |
|
SubField 3A |
This optional subfield may
specify a proper motion in RA. It is in milliarcseconds per
year on the sky, i.e., ΔRA*cos(dec). |
| Field 4 |
Astrometric Declination
position coordinate in equinox given by Field 6 always at epoch 2000, given as D:M:S. |
|
SubField 4A |
This optional subfield may
specify a proper motion in Dec. It is in milliarcseconds per
year on the sky |
Field
5
|
Magnitude
of the object. |
Field
6
|
This
optional field is the reference epoch. It is assumed to be
2000 if absent |
| Field 7 depends on SubField 2A |
| If SubField 2A is G
or H |
Field
7
|
Galaxy
major axis, in arcseconds |
|
SubField 7A |
Galaxy minor axis, in arcseconds |
|
SubField 7B |
Major axis position angle, in
degrees East of North |
| If Subfield 2A is B
or D |
| Field
7 |
star
pair separation, in arcseconds
|
|
SubField 7A |
reserved, set to 0 |
|
SubField 7B |
position angle, in degrees East
of North |
| Otherwise Field 7 is
optional but if present |
| Field
7 |
size of
the object, in arcseconds. It is assumed to be 0 if absent. |
If
Field 2 is
B the object is a true
binary pair and
the
following fields and subfields are defined.
|
SubField 2A |
An optional SubField 2A can be
added to further define an binary class code, consisting of
one character from the following list. This scheme is taken from the
Washington Multiplicity catalog for compliance with the IAU 2003
recommendation.
a
|
Astrometric binary
|
c
|
Cataclysmic variable
|
e
|
Eclipsing binary
|
x
|
High-mass X-ray binary
|
y
|
Low-mass X-ray binary
|
o
|
Occultation binary
|
s
|
Spectroscopic binary
|
t
|
Single-line spectroscopic
binary
|
u
|
Double-line spectroscopic
binary
|
v
|
Spectrum binary
|
b
|
Visual binary
|
d
|
Visual binary with common proper motion
|
q
|
Visual binary - optical
|
r
|
Visual binary - physical
|
p
|
Exoplanet
|
|
|
SubField 2B |
Up to two characters to specify
the spectral class of the primary star, typically one letter followed
by one numerical subclass designator. Two examples are O and G3. |
|
SubField 2C |
Up to two characters to specify
the spectral class of the secondary star,
typically one letter followed by one numerical subclass designator.
Two examples are O and G3. |
| Field 3 |
RA
position coordinate, given as H:M:S. |
|
SubField 3A |
This optional subfield may
specify a proper motion in RA. It is in milliarcseconds per
year on the sky, i.e., ΔRA*cos(dec). |
| Field 4 |
Declination
position coordinate, given as D:M:S. |
|
SubField 4A |
This optional subfield may
specify a proper motion in Dec. It is in milliarcseconds per
year on the sky |
Field
5
|
Magnitude
of each star in the pair. |
|
SubField 5A
|
Magnitude of the primary star
|
|
SubField 5B
|
Magnitude of the secondary star
|
Field
6
|
This
optional field is the reference equinox year. It is assumed to be
2000 if absent |
Field 7
|
This field may contain
either 3 or 6 subfields (one or two triples of year/separation/position
angle)
or 7 subfields (orbital elements).
|
|
If 3 or 6 subfields,
they define positions grouped as the following triplets:
|
|
SubField 7A/D |
Year of the separation and position angle given
in the next two fields, decimal year or month/day/year |
|
SubField 7B/E |
Separation, arc seconds
|
|
SubField 7C/F |
Position angle, degrees E of N, referenced to
equinox in field 6
|
|
If 7 subfields, they
define a
true orbit:
|
|
SubField 7A
|
Semi-major axis, arcseconds
|
|
SubField 7B |
Inclination from plane of sky, degrees
|
|
SubField 7C |
Longitude of node, degrees
|
|
SubField 7D |
Eccentricity
|
|
SubField 7E |
Epoch of periastron, decimal year or
month/day/year
|
|
SubField 7F |
Argument of periastron, degrees
|
|
SubField 7G |
Period. Units are designated by suffix y
for years, d for days, or h for hours. If no
designation the default is years.
|
If Field
2 is e the object type
is
elliptical heliocentric (eccentricity < 1) and the remaining fields
are defined as follows:
Field
3
|
i =
inclination, degrees |
Field
4
|
O =
longitude of ascending node, degrees |
Field
5
|
o =
argument of perihelion, degrees |
Field
6
|
a = mean
distance (aka semi-major axis), AU |
Field
7
|
n = mean
daily motion, degrees per day (computed from a**3/2 if
omitted) |
Field
8
|
e =
eccentricity, must be < 1
|
Field
9
|
M = mean anomaly,
i.e., degrees from perihelion |
Field
10
|
E = epoch date,
i.e., time of M |
|
SubField 10A |
First date these elements are
valid, optional
|
|
SubField 10B |
Last date these elements are
valid, optional
|
Field
11
|
D = the equinox
year, i.e., time of i, O and o |
Field
12
|
First component of
magnitude model, either g from (g,k) or
H from (H,G). Specify which by preceding the number with a "g"
or an "H". In absence of either specifier the default is (H,G) model.
See Magnitude models. |
Field 13
|
Second component of
magnitude model, either k or G
|
Field 14
|
s =
angular size at 1 AU, arc seconds, optional |
You may have other parameters
available
for elliptical orbits that can be converted into these. The
following relationships might be useful:
P
= sqrt(a*a*a)
p = O + o
n = 0.9856076686/P
T = E - M/n
q = a*(1-e)
AU = 149,597,870 km = 92,955,621 U.S. statute miles
where
P = the orbital period,
years;
p = longitude of
perihelion, degrees
T = epoch of perihelion
(add multiples of P for desired range)
q = perihelion distance, AU
Note that if you know T you can then set E = T and M = 0.
If
Field
2 is
h the object type
is
hyperbolic heliocentric (eccentricity > 1) and the remaining fields
are defined as follows:
Field
3
|
T = date
of the epoch of perihelion |
|
SubField 3A |
First date these elements are
valid, optional |
|
SubField 3B |
Last date these elements are
valid, optional |
Field
4
|
i =
inclination of orbital plane to ecliptic, degrees |
Field
5
|
O =
longitude of ascending node, degrees |
Field
6
|
o =
argument of perihelion, degrees |
Field
7
|
e =
eccentricity, must be > 1
|
Field
8
|
q =
perihelion distance, AU |
Field
9
|
D = the
equinox year (i.e., time of i/O/o) |
Field
10
|
g
component of magnitude model. See Magnitude
models. |
Field 11
|
k component of magnitude
model
|
Field
12
|
s =
angular size at 1 AU, arc seconds, optional |
As with elliptical elements, other
parameters might be available. The relationships are generally the
same, except:
q
= a*(e-1)
If
Field 2 is
p the object type is parabolic
heliocentric (eccentricity exactly equal to 1) and the remaining
fields are defined as follows:
Field
3
|
T = date
of epoch of perihelion |
|
SubField 3A |
First date these elements are
valid, optional |
|
SubField 3B |
Last date these elements are
valid, optional |
Field
4
|
i =
inclination, degrees |
Field
5
|
o =
argument of perihelion, degrees |
Field
6
|
q =
perihelion distance, AU |
Field
7
|
O = longitude of
ascending node, degrees |
Field
8
|
D = the equinox year
(i.e., time of i/O/o). |
Field
9
|
g component of
magnitude model. See Magnitude models. |
Field 10
|
k component of magnitude
model |
Field
11
|
s = angular size at
1 AU, arc seconds, optional |
If
Field
2 is
E (note upper
case)
the object type is Earth satellite and the remaining fields are defined
as follows:
Field
3
|
Epoch of the other
fields |
|
SubField 3A |
First date these elements are
valid, optional |
|
SubField 3B
|
Last date these elements are
valid, optional |
Field
4
|
inclination, degrees |
Field
5
|
RA of ascending
node, degrees |
Field
6
|
eccentricity, must
be < 1 |
Field
7
|
argument of perigee,
degrees |
Field
8
|
mean anomaly, degrees |
Field
9
|
mean motion, revs/day |
Field
10
|
orbit decay rate,
revolutions/day^2 |
Field
11
|
integral reference
orbit number at Epoch
|
Field
12
|
drag coefficient,
1/(earth radii); optional |
XEphem arbitrarily assigns all Earth
satellites a visual magnitude of 2.0.
XEphem can also read files directly containing the venerable
Two-Line-Element (TLE) format. See next section for details.
If not specified explicitly in the edb entry, XEphem assigns the valid range
of dates for satellite elements to the greater of 100 days or the time
required for the mean motion to change by one percent either side of the
element epoch.
If
Field
2 is
P (note upper
case)
then
Field 1 must be the name
of
a built-in object for XEphem and no other fields are defined. The
following names are recognized:
Sun
Moon
Mercury
Venus
Mars
Phobos
Deimos
Jupiter
Io
Europa
Ganymede
Callisto
Saturn
Mimas
Enceladus
Tethys
Dione
Rhea
Titan
Hyperion
Iapetus
Uranus
Ariel
Umbriel
Titania
Oberon
Miranda
Neptune
Pluto
<IP_ADDRESS> Magnitude models
The g,k magnitude model
requires two parameters to be specified. One, the absolute magnitude,
g, is the visual magnitude of the object if it were one AU from both
the Sun and the Earth. The other, the luminosity index, k,
characterizes the brightness change of the object as a function of its
distance from the Sun. This is generally zero, or very small, for
inactive objects like asteroids. The model may be expressed as:
m
= g + 5*log10(D) + 2.5*k*log10(r)
where:
m
= resulting visual magnitude
g = absolute visual
magnitude
D = comet-earth distance,
in AU
k
= luminosity index
r
= comet-sun distance.
The H,G model also requires
two parameters. The first, H, is the magnitude of the object when one
AU from the Sun and the Earth. The other, G, attempts to model the
reflection characteristics of a passive surface, such as an asteroid.
The model may be expressed with the following code fragment:
beta
= acos((rp*rp + rho*rho - rsn*rsn)/ (2*rp*rho));
psi_t =
exp(log(tan(beta/2.0))*0.63);
Psi_1 = exp(-3.33*psi_t);
psi_t =
exp(log(tan(beta/2.0))*1.22);
Psi_2 = exp(-1.87*psi_t);
m = H + 5.0*log10(rp*rho) -
2.5*log10((1-G)*Psi_1 + G*Psi_2);
where:
m =
resulting visual magnitude
rp = distance from
sun to object
rho = distance from
earth to object
rsn = distance from
sun to earth
Note that neither model takes into account the phase angle of sun light.
7.1.3 Notes
XEphem uses a different window to manage Field
star catalogs.
XEphem ships with a few perl scripts which might be helpful for
converting databases in other formats into XEphem format. These
scripts are in the tools/ directory of the source distribution tree.
7.1.4 Two-line Earth
satellite element sets
XEphem supports reading files which contain Earth satellites defined
using the the NORAD "two-line element" set format, or TLE. Because the
TLE format is quite rigid and includes a checksum within each line,
XEphem is able to search files containing other arbitrary text and find
each properly formatted TLE contained therein. Follows is a description
of the TLE. Note the line immediately preceding the TLE, line "0", is
assumed to contain a common name for the satellite, this line is only
used if the following two lines conform to TLE.
Data for each satellite consists of three lines in the following
format:
AAAAAAAAAAAAAAAAAAAAAAAA
1 NNNNNU NNNNNAAA NNNNN.NNNNNNNN +.NNNNNNNN +NNNNN-N +NNNNN-N N NNNNN
2 NNNNN NNN.NNNN NNN.NNNN NNNNNNN NNN.NNNN NNN.NNNN NN.NNNNNNNNNNNNNN
Line 0 is a twenty-four character name.
Lines 1 and 2 are the standard Two-Line Orbital Element Set Format
identical to that
used by NORAD and NASA. The format description is:
| Line 1 |
| Column |
Description |
| 01 |
Line Number of Element Data |
| 03-07 |
Satellite Number |
| 08 |
Classification (U=Unclassified) |
| 10-11 |
International Designator, last two digits of launch
year, 2000+ if < 57. |
| 12-14 |
International Designator, launch number of the year |
| 15-17 |
International Designator, piece of the launch |
| 19-20 |
Epoch Year, last two digits of year, 2000+ if < 57 |
| 21-32 |
Epoch Day of the year and fractional portion of the day |
| 34-43 |
First Time Derivative of the Mean Motion |
| 45-52 |
Second Time Derivative of Mean Motion (decimal point assumed) |
| 54-61 |
BSTAR drag term (decimal point assumed) |
| 63 |
Ephemeris type |
| 65-68 |
Element number |
| 69 |
Checksum (Modulo 10)
(Letters, blanks, periods, plus signs = 0;
minus signs = 1)
|
| Line 2 |
| Column |
Description |
| 01 |
Line Number of Element Data |
| 03-07 |
Satellite Number |
| 09-16 |
Inclination [Degrees] |
| 18-25 |
Right Ascension of the Ascending Node [Degrees] |
| 27-33 |
Eccentricity (decimal point assumed) |
| 35-42 |
Argument of Perigee [Degrees] |
| 44-51 |
Mean Anomaly [Degrees] |
| 53-63 |
Mean Motion [Revs per day] |
| 64-68 |
Revolution number at epoch [Revs] |
| 69 |
Checksum (Modulo 10) |
When reading a TLE entry, XEphem assigns the valid range of dates for a set of
elements to the greater of 100 days or the time required for the mean motion
to change by one percent either side of the element epoch.
7.2 Index
This
window shows a list of all objects currently loaded into memory sorted
by name. Or, by chosing a toggle button across the top, the list can
be restricted to just deep sky, stellar, binary systems, solar system
and
Earth
satellites. The list does not include Favorites.
Each object name, including all alternate names, are in the scrolled
list on
the right. Clicking an arrow
button moves the list by one object up or down; clicking above or below
the thumb
control scrolls the list so that the top object moves to the bottom or visa versa. Clicking on an object
displays its defining parameters in the box to the left, and also
displays its .edb file format entry in the read-only text field below.
The list of objects may be searched by entering a glob pattern in the Search field then
typing Enter or clicking Search. If more than one object name matches,
clicking Search again scrolls to the next candidate; the search wraps
back to the front when no more are found.
Buttons across the bottom function as follows:
Sky Point
This will mark the object currently selected in the
Sky
View, repointing if necessary to move it into the field of
view.
Show in Gallery
If this object is in the
Gallery, this button will be available and will
display the object.
Save as Favorite
This button will add the object
currently
selected to the list of
Favorites.
Tel Goto
This will send the object currently
selected to the
Telescope control
system. Whether this button is active depends on the state of the
telescope control subsystem when the Index window was opened. If the
button state is incorrect, close and reopen the Index window.
7.3 Favorites
This
window allows you to add, arrange, remove and temporarily deactivate an
arbitrary collection
of XEphem objects, called Favorites. Once defined as a Favorite, the
object remains available whether or not its original database file is currently loaded.
Favorites have special significance in several places throughout
XEphem. For example the rows in the Data Table
and in the Night at a Glance windows are
exactly those of the Favorites. The Earth view
shows those Favorites which are satellites. Favorites are available
very
easily in the Favorites menu in the Sky View.
And the Solar System view displays those
Favorites
that are within the solar system.
Objects may be added to the list of Favorites in several ways:
- from the Data
»
Index
window by browsing the objects currently loaded in memory then clicking
Favorite;
- from buttons labeled Favorite located in several dialogs
throughout XEphem;
- from buttons in the popup menus of several views when clicked
over displayed objects; and
- by entering its .edb format definition in the text field near the
bottom of the Favorites window and clicking Add edb.
Note this field may also be used to edit an existing Favorite in-place.
Each entry in the Favorites list shows its complete .edb format
definition. Each entry has the following controls:
Del
removes the entry from the Favorites
list
Up and Down arrow buttons
move the entry up and down to arrange
the Favorites into any designed order. This is useful where Favorites
define rows such as in the
Data Table and
Night at a Glance windows.
Use
specifies whether to use or hide the
entry from
the rest of XEphem without actually Deleting it.
The buttons across the bottom allow you to Save the current set
of Favorites to a file and later Load them again.
The suffix of these files must be .fav and will be added
automatically if not included in the file named in the text field. When
XEphem first starts, it automatically
loads the file named in the Save text field. To save this file name, go
to Preferences » Save
and Save
the XEphem*Favorites*File resource under the Favorites category.
7.4 Download
This
window provides an easy means to download from the Internet to disk and
simultaneously
load into memory any file which contains objects defined in either
XEphem's .edb format or the NORAD 2-Line Element (TLE) format commonly
used for Earth satellite. The file is saved in the Private directory, converted to .edb
format if it is not already.
Several particularly useful sites as of this build are already entered.
The first three are from Dr. TS Kelso's Earth satellite lists at celestrak.com. The other four are
the Minor Planet Center's lists of hot comets and unusual asteroids
specially formatted for XEphem.
Click Get beside the desired
catalog to download the file to the Private directory and
simultaneously load into XEphem memory.
Special files created by the Minor Planet Center
and Lowell
Observatory may also be downloaded. Each organization maintains
extensive lists of all known asteroids and produces on a regular basis
Keplarian orbital elements precessed to the current date. Both are of
excellent quality. When the Get
button is clicked, XEphem downloads the appropriate file, uncompresses
it, reformats it to .edb format and splits the results into two files
for convenience. One file will contain all asteroids which can ever
become brighter than magnitude 13, and the other (with a "_dim" suffix)
contains all the rest. All files are created in the user's Private
XEphem directory. The real work is performed by two perl scripts,
mpcorb.pl and astorb.pl, respectively. These may be run independently
of XEphem if desired.
7.5 Field Stars
This window allows you to control
which
field star
sources you wish to use. The window is accessible from the Main window
as well as from the Control menus of most graphical views.
XEphem uses the term "field star" to refer to the huge numbers of faint
stars visible in any real world view of the sky. Field stars are
generally far more numerous than could be reasonably accommodated in
the XEphem *.edb database format. For this reason they are stored and
made available in their own special compact forms for utmost
efficiency. The downside to this approach is that field stars are not
included in the totals presented by the Data » Files window nor
are they available for searching or inspection using the Data » Index window.
This results in little loss of generality, however, since (once
found!) they may be assigned to the user Favorites.
The controls in the Field Stars setup window are grouped into
categories, depending on the basic source of the stars, as follows:
7.5.1 Hubble GSC
The Hubble Guide Star Catalog is a seminal work created by the Space
Telescope Science Institute to support the Hubble Space telescope. It
contains from 13 million unique stars, or about 300 stars per square
degree of sky.
ASP CDROM Directory
This choice enables reading field stars
from the Hubble Guide Star Catalog made available some years ago
on two CDROMs published by the Astronomical Society of the
Pacific. Mount a CDROM somewhere onto your filesystem, type the
name of the mount directory in the text field provided then turn
this option on and press Apply. Note that XEphem assumes your CDROM
driver removes the trailing ";1" from all filenames.
Local Cache Directory
This choice enables reading GSC field
stars from your local disk. If this option is on along with the
CDROM option, then as requests are satisfied from the CDROM a
compact form of the same data will be written to files below the
directory named in this option. Then the next time the same field stars
are needed, and this option is on, they will be obtained from the
local disk files rather than the CDROM. In fact, the CDROM is not
needed
or used if the local disk contains all the stars for any given
access. The entire 2 CDROM set loads onto disk in this format in
some 180 MB. The default path of the directory which holds the
disk version is "catalogs/gsc" off the Shared directory. Note:
There is also a utility in the tools/gsc directory, gscload, with
which you may preload any entire CDROM segment at once if desired.
These files are already included in te commercial version of
XEphem.
Internet to xephemdbd
This choice is to use the Internet to
access an XEphem GSC server. To use this source, select this
option and type the URL to the remote xephemdbd.pl in the text
field provided.
GSC 2.2 Directory
This choice enables using a local copy
of the GSC <IP_ADDRESS> catalog in xe3 format. This catalog only contains
stars between magnitude 10 and 18.5, so it must be used in conjunction
with
an additional catalog for completeness. The Hipparcos catalog is an
ideal companion and is automatically chosen as a convenience.
7.5.2 USNO A or SA catalogs
Root directory
This choice of field stars supports the SA and the A series of
astrometric catalogs produced in recent years by the US Naval
Observatory. The SA2.0 for example, includes some 54 million stars,
spatially sampled so there is about 1,300 stars per square degree of
sky. Note that such a uniform distribution does not "look" much like
the real sky, but it is great for its intended use as an astrometric
mesh for comet hunters or such. To order these catalogs, see
http://psyche.usno.navy.mil/pmm.
If you have such a catalog, simply enter the name of its base directory
and toggle this switch on. The default assumes a symbolic link,
"catalogs/usno" off the shared directory. The suggested citation for
SA1.0 follows:
Monet, D., Bird, A., Canzian, B.,
Harris, H., Reid, N., Rhodes, A., Sell, S., Ables, H., Dahn, C.,
Guetter, H., Henden, A., Leggett, S., Levison, H., Luginbuhl, C.,
Martini, J., Monet, A., Pier, J., Riepe, B., Stone, R., Vrba, F.,
Walker, R. 1996, USNO-SA1.0, (U.S. Naval Observatory, Washington
DC).
This catalog has been included with permission of USNO as long as
we mention the following stipulations:
It may not be the latest version,
check
with http://ad.usno.navy.mil.
If you paid for XEphem, you paid for
the software, not this catalog. The catalog is available free from
the USNO.
Inclusion of the SA2.0 catalog does
not
imply an endorsement of XEphem by USNO; nor did I have privileged
access to the catalog; nor does the US Government affirm or
guarantee that XEphem works properly in any way.
7.5.3 Proper Motion catalogs
These large catalogs include information regarding proper motion.
Two such catalogs are currently available ready for XEphem. You may
only use one at a time, by choosing the corresponding toggle
PPM catalog
This is the Positions and Proper Motion
catalog of S. Roeser and U. Bastian, Astronomisches
Rechen-Institut, Heidelberg, published in 1990. The PPM includes
468,586 stars rather evenly distributed throughout both
hemispheres. This averages out to more than 10 stars per square
degree. The set here includes the original North and South
editions plus the extended supplement. The set includes more than
99% of the stars in the original SAO catalog and some 70% of the
Henry Draper Catalogue (HD). While the SAO catalog is more or less
complete to V=9, with stars as faint as V=10, the PPM catalog is
fairly complete to V=9.5, and goes somewhat deeper than V=10.
Hipparcos and Tycho-2
This catalog is a combination of the
Hipparcos and the Tycho-2 astrometric catalogs published by the
European Space Agency. This catalog contains all Hipparcos stars
for which astrometric and magnitude values are assigned, and all
additional non-redundant entries from the Tycho-2 catalog except
multiple-component entries. There is a total of some 2.5 million
stars, or about 60 stars per square degree. One example of a star with
high proper motion is Groombridge 1830 (HD 103095), in Ursa Major,
near 11h53m 37d44m. For a nice discussion see Burnham's Celestial
Handbook, Volume III, page 1978. By comparing its position in either
PM catalog with the same entry from the GSC one can deduce this
particular GSC field was evidently taken in early 1983.
UCAC
This choice allows using the USNO Astrographic catalog with XEphem. For
more information on this catalog please refer to
here.
As of release UCAC4, the directory specified must be that which contains
the u4b and u4i directories. In turn, u4b must contain all 900 z files and
u4i must contain u4index.unf and u4hpm.dat.
7.5.4 Skip likely duplicates
All of the above may be used together with the regular database
facility of XEphem. If this option is on, XEphem eliminates what
appears to be redundant entries for the same star from the various
catalogs. Two stars are considered the same if their positions match
within the given number of arcseconds and their brightnesses differ by
less than the given number of magnitudes. (The generous default
magnitude tolerance is because the GSC and the PPM use varying
filters).
When deciding on the final selection for such duplicate entries the
highest priority is the local database, then the HD or SAO entry,
then the PPM entry, then Hipparcos, then Tycho and finally the GSC
entry.When you have made the desired entries, pressing Apply will attempt to check each
filename, directory and Internet choice, as appropriate. The cursor
will be a Watch while the tests are in progress. If something does not
seem correct, a warning window will appear and the option will be
turned back off. If everything seems to be operating correctly, you
are in business. The Ok button
does the same thing but then also closes the window if they all
succeed.
7.5.5 Notes
If at any time something goes wrong during the acquisition of any
Field Stars from any View, the responsible option in that view is also
turned off automatically. The problem should be corrected and Field
stars turned on again.
All field star sources will silently enforce limits on the total number
of stars they yield for any query. As of this writing, local queries
except USNO are limited to 30 degrees; USNO are limited to 15 degrees;
network queries impose various limits.
8.0 Preferences
The simple choice preferences are covered in the Main Window section.
See Preferences menu,
8.1
Fonts
This
window lets you change most of the fonts used by XEphem. The basic
technique is to specify a font, use the four toggle buttons to choose
which action to take then perform the action in a particular font
context by clicking in the menus accessed from the menubar across the
top.
To browse the available fonts, type a pattern in the field provided and
click Search. This will
display
the names of all fonts matching a pattern. To see all available fonts,
use the wild card pattern of a single star (*). To be more specific,
specify the fields desired and fill the gaps between with the star
wildcard. See the next section for a description of each field.
Clicking a font in the top list will display a sample and its full name
in the region at the bottom.
The Buttons, Text and Other menus in the menu bar across
the top provide ways of referring to several font contexts. The four
toggle buttons just below the menu bar determines what happens when one
of these context menu buttons is clicked, as follows:
Get current
When this toggle is active, clicking a
context menu button will cause the name of the current font for that
context to be displayed in the pattern field and history list.
Get default
When this toggle is active, clicking a
context menu button will cause the name of the last saved default
font for that context to be displayed in the pattern field and
history list.
Set
When this toggle is active, clicking a
context menu button will cause the font named in the pattern field
of this window to be applied to that context throughout XEphem.
Restore default
When this toggle is active, clicking a
context menu button will cause its last saved font value to be
reinstated through XEphem.
Fonts that have been changed from their default values are tagged in
the Preferences » Save
window (when opened or after you do a Refresh). This allows you to Save
the new fonts set here permanently. If you do not Save it, the change
only effects XEphem until you exit.
There are a few situations scattered around within XEphem for which
changing fonts at runtime from this window does not work perfectly.
For example, changing to a smaller font does not shrink some windows
as much as you might expect. Such anomalies are known challenges and
do not indicate serious problems. After Saving the fonts and
restarting XEphem, all will work again as expected.
8.1.1 XLFD
The font names are in the format called X Logical Font Description.
There are 15 fields separated by hyphens. The fields are as follows:
- Foundry
The organization that digitized the font data.
Family
- The commercial name of the font.
Weight
- The relative weight of the font, such as bold, medium or regular.
Slant
- A code indicating the slant:
r Roman (no slant)
i Italic (slant left)
o Oblique (slant left)
Set Width
- The width with respect to what the foundry considered normal.
Choices include normal, condensed, narrow, double.
Additional Style
- Anything else needed to uniquely identify the font, such as sans
or serif.
Pixel Size
- The height of an em in
pixels.
Point Size
- The height of an em in
tenths of a point, where one point is 1/72 inch.
Horizontal Resolution
Vertical Resolutoin
- The resolution of the device for which the font was designed, in
pixels-per-inch.
Spacing
- A code indicating the spacing between characters in the font:
M Monospaced (fixed pitch)
P Proportional spaced (variable pitch)
C Character cell (each character occupies the same size box)
Average Width
- Average width of all characters in the font, measured in tenths
of
a pixel.
Registry
Enoding
- The registration authority and their name for the character set
from which the characters in the font are drawn. For example ISO8859-1,
also known as Latin-1.
Scalable fonts are indicated by 0 for point size, pixel size, x and y
resolution and average width (fields 7, 8, 9, 10 and 12). To choose a
specific scalable font, specify desired values for some but not all of
these fields, letting the system fill in the others.
8.2
Colors
This window lets you change most of the
colors used by XEphem. The basic technique is to use the four toggle
buttons to choose which action to take then perform the action in a
particular color context by clicking in the menus accessed from the
menubar across the top.
The possible actions are as follows:
Get current
When this toggle is active, clicking a
color context menu button will cause the current color for that
context to be displayed in the color patch in the lower right corner
of this window.
Get default
When this toggle is active, clicking a
color context menu button will cause the last saved default color
for that context to be displayed in the color patch in the lower
right corner of this window.
Set
When this toggle is active, clicking a
color context menu button will cause the color currently being
displayed in the color patch of this window to be applied to that
context throughout in XEphem.
Restore default
When this toggle is active, clicking a
color context menu button will cause its last saved color to be
reinstated.
Above the color patch are three sliding scales that allow you to define
a color using either Red+Green+Blue or Hue+Saturation+Value, depending
on the toggle. Each scale ranges from 0 through 255. Hue is the basic
spectral color, where 0 is red, 85 is green, 170 is blue. Saturation
is the amount of color purity, where lower values mix in more white.
Value is like brightness, where 0 is totally black.
The text field at lower left allows you to type a color using one of
the standard descriptive names, such as "steel blue", or in hex RGB
notation, for example #ff0000 for pure red, #00ff00 for pure green
#0000ff for pure blue. After typing the desired value, press Enter to
set the scales and see the color in the patch. This field is also set
automatically when the scales are used to set a color, during Grabbing
(see next), and when a color context is retrieved.
The history list in the lower left stores each color name that is used
from the name field, making it easier to reuse a color. Selecting a
name
will copy it to the name field and show it in the color patch. You can
select history entries with the mouse, or by browsing with the Up and
Down keyboard arrow keys.
8.2.1 Colors Control menu
Night
mode
This changes the XEphem background to
black, and uses the Night vision color for all text. Clicking this
back off will restore the previous colors. Note that when Night vision
is on, you may not change the colors it effects. This is to eliminate
confusion with regards to whether or not they are new in the Save
window.
Grab
color
Press this button and the cursor will
change to a crosshair. Move the cursor around on the screen and the
color of the pixel under the crosshair will be displayed; press
Button1 to capture the color and resume normal cursor operation.
Clear
history
Erases all entries in the History list.
When a color context is changed, it also changes the corresponding
resource. In the Preferences
» Save window you will notice that the resource becomes
marked as Modified (when opened or after you do a Refresh). This
allows you to Save the new color choice permanently. If you do not
Save it, the change only effects XEphem until you exit.
8.2.2 Star colors
XEphem assigns colors to stars based on their spectral classification.
The default colors were chosen based on work done by Mitchell Charity.
The colors are specified using X Resources. The resource names each
begin with "XEphem.starSpect" followed by one or two characters. The
value of the resource is the color. The following table shows the
default spectral color resources built into XEphem:
XEphem Resource Name
|
Default Color Value
|
| XEphem.starSpectO |
#9bb0ff |
| XEphem.starSpectB |
#aabfff |
| XEphem.starSpectA |
#cad7ff |
| XEphem.starSpectF |
#f8f7ff |
| XEphem.starSpectG |
#fff4ea |
| XEphem.starSpectK |
#ffd2a1 |
| XEphem.starSpectM |
#ffcc6f |
| XEphem.starSpectN |
#ff8f2c |
| XEphem.starSpectS |
#ffc574 |
| XEphem.starSpectC |
#ff9e40 |
| XEphem.starSpectT |
#ffd19a |
| XEphem.starSpectW |
#c4c4ff |
XEphem uses the closest entry with matching first character. If no
entry is found with matching first character then white is used and a
message is added to the System log. The
spectral color resource values may be edited or additional resources
can
be added but this must be done by hand, there is no GUI support
available. Always edit the XEphem resource file while XEphem is not running to avoid any chance of
conflict.
8.3 Save
This window displays all of the
options,
settings and controls, collectively called Preferences, throughout
XEphem that may be saved and
reinstated next time the program is started. XEphem has many such
preferences, so
they are separated into categories in this window for easier
management. Each category may be expanded or collapsed using the
+/- toggle square to show each individual preference.
Preferences are saved using the standard Resource mechanism provided by
the X Window System. These resources are saved in the file XEphem
located in the Private directory.
Each preference may be tagged for saving. The toggle at the top
controls whether all tagged preferences will be Autoatically saved
when XEphem is Quit.
Preferences have been divided into two classes.
Major: In the opinion of the author these
preferences are sufficiently interesting that they are likely to be
worth saving and automatically restoring between one invocation of
XEphem and the next.
Minor: Everything else, presumably less critical in nature. It
is expected that you are likely to
change these preferences frequently in due course while operating
XEphem yet they do not cause major effects on program behavior so
saving them at
any one particular setting is not especially compelling. Minor
preferences are things like window size and position, scale settings
which
only effect views, and all of the Sky View Filter and Option settings.
This distinction is of course rather arbitrary so please take
care when changing and saving preferences so the ones you want are
saved.
The number of preferences in each class currently tagged
for saving is indicated by messages near the top.
The scrolled area can display each preference, whether it is tagged for
saving and the ability to change whether it is tagged. Each category of
preference can be expanded for more detail using the +/- toggle square.
In the expanded view, each preference and its value are
shown exactly
as it will appear in the disk file if Saved. Those preferences
which differ from the last time they were Saved, or since XEphem was
started if no Save has yet occurred, are marked with a bullet. Major
preferences are marked with a solid bullet, Minor preferences with an
hollow
bullet. A toggle next to each preference allows individual selection
over whether the preference will be written to disk on the next Save.
After each Refresh, the toggles are set for those preferences found to
have changed since the last Save if their class is set to be
automatically tagged. Each toggle may be changed manually in either
direction to override this automatic behavior on an individual basis
if desired but not these will be overridden with the next Refresh.
In the collapsed view, if at least one Major preference is out of date
in a category, a solid bullet is placed next to the category heading;
otherwise if at least one Minor preference is out of date a hollow
bullet is used.
Note that the information in this window does not
automatically track changes in preferences as XEphem is used. You must
use Refresh to update the status manually when desired. In particular,
the values which are Saved are what they were the last time Refresh
was performed, not what they actually are at the moment Save is
activated.
Save now
Write each tagged preference to disk to
the XEphem resource file.
If the file already exists, it will first be copied to XEphem.bak in
the same directory. If a preference already exists in the file it will
be
edited in-place, otherwise a new entry is added at the bottom. Other
lines in the file are left unchanged. After using Save, all preferences
will be considered up to date, even if they were not selected to be
written to the preference file.
N.B. The values saved are as they
appear in this window, which may be different from their current
value if they have changed since the last Refresh.
Refresh
Update the changed and save status of
each preference. This refresh action also
happens automatically after a Save is performed and just before
XEphem quits when deciding which preferences to save if the Automatic
saving option is enabled.
9.0 Multifunction Tools
The tools in this section are used in several different places
throughout XEphem. The descriptions here are generic. If there are any
special issues when used in certain contexts they will be described in
the appropriate sections elsewhere.
9.1 Trails
This
window allows you to define a set of time values spaced at regular
intervals before and after the current XEphem time and define which
and in what manner values will be annotated with a time stamp.
This is a general purpose facility used in several places throughout
XEphem, generally for the purpose of establishing a trail of object
motion. This description will be of a general nature.
Six format parameters must be specified:
Orientation
This choice determines where the
stamps
appear in relation to their corresponding position mark. The first
several options should be self-explanatory. The last two, Path-left and
Path-right, cause the time stamps
to be placed to the left or right side of the trail path, as one would
perceive these directions when traversed in forward time order. In
no case are the time stamps ever drawn to require you to turn your
head more than 90 degrees left or right.
Interval
This is the time interval between each
step. Choose from among several predefined intervals or choose Custom
and enter any desired interval
in the space provided. It is okay to specify more than 24 hours to
achieve intervals of several days. It is also okay to specify negative
values to run time backwards.
Label
This choice determines which intervals
will to be labeled with a time stamp. Choose from among several
options or choose None if no labeling
is desired. Times will be printed surrounded by parentheses if the
object is an Earth satellite and it is eclipsed.
Format
This choice determines the format in
which to display
each time-stamp. Choose Hour:Minute
with or without Seconds or the date formatted as per the
Preferences » Date formats
option in the Main menubar, see
Preferences.
Font
This choice sets the size of the
annotation text font.
Start
This choice specifies how the first
time value is derived from the current XEphem time. The lower right
radio box offers several methods of determining the beginning of the
first time interval. The idea here is generally to match the time
values of each time mark with the precision implied by the format, but
to allow other options for special situations.
Whole min rounds the current
XEphem time forward to the next whole minute, if necessary;
Whole day rounds to the next
whole day.
Whole interval rounds to the
next whole multiple of whatever time interval is set (as specified
in the Intervals choices).
Now means to begin with the
current XEphem time without any initial changes.
Two scales near the bottom specify the number of tick marks to create
before and after the starting time.
Once the choices are set up as desired, Ok will create the trail and the
window will disappear. Apply
will create the trail but the window will remain up for further use. Close just dismisses the window
without creating a trail.
Even with all this flexibility pleasingly annotated trails are not
trivial to generate. It is hoped that a little experimentation can
yield acceptable results in most cases. Note that this general trail
facility does not provide close coupling with the view being
supported. For example, some views do not support setting a trail for
an object which has changed while the Trail Setup is up. Also, views
may vary in their support of having trails defined while they are not
visible. Each view may establish its own initial default values but
changes usually remain in effect for subsequent instances of Trail
Setup windows from the same view. Some views permit more than one
Trail Setup to be active at one time. In short, the operational
boundary conditions vary by view.
The settings for each view context may be saved using
Preferences » Save.
9.2 Printing
This
window lets you print the current view or save it to a file. In either
case the format used is Postscript.
Title
If you enter a string in the text
field
labeled Title, the string will be printed centered across the top of
the page.
Color
Black
The top left pair of toggle buttons
allow you to choose whether color commands will be included in the
Postscript generated.
Letter
A4
The center pair offer the choice of US
Letter size 8½x11" with ¾" margin or ISO A4 210x297mm
with 15mm margin.
Thin lines
Thick lines
The right pair offer the choice of
drawing with very thin lines or somewhat thicker lines.
Save to file
If you choose to Save to a file, turn
on that toggle button and enter the desired file name in the text
box to the right of the toggle button. Unless begun with a / the
file name is in the
Private directory.
Print command
If you choose to print directly to the
printer, turn on that toggle button and enter a command which will
print a Postscript file on your system. The command should expect
the name of a file to print as its first and only argument. A
temporary file will automatically be created for this command and
deleted when printing is completed. You can also enter a command
here that will display the file, such as gv to preview the file then
and print from there.
When ready, click Ok. To avoid
printing, press Cancel. If
your
current viewing fonts are not available for printing, error recovery
will depend upon your local print system.
9.3 Annotation
This window allows you to add your own text
and lines to any graphical
view. Annotation locations are saved in the world coordinates of the
view. For example, in the Earth view they are saved in Lat and Long. In
the Sky View, they are saved in the current display mode, that is,
either RA/Dec or Alt/Az. The window shows which view each annotation
refers to.
You may Save the current set of annotations to the specified
file or Load a set by selecting from the files presented in the
pop-down menu. Annotation files use the suffix .ano. XEphem tries to
automatically load the file specified in the Save field when it starts.
This
file name can be saved in the Preferences » Save window in
the Annotation section.
To add a new annotation entry:
- click New to create a blank entry,
- type in the desired text,
- click Place to begin the placement procedure,
- move the cursor to position the text where desired,
- click and hold to anchor the text and begin drawing a line,
- move the pencil cursor to position the far end of the line as
desired,
- release.
To move an existing entry, click Place
again and proceed as above with step 4.
To draw just a line with no text, leave the text field blank.
To place text with no line, immediately release after anchoring the
text.
To change just the text of an existing entry, edit the text and type
Enter.
To temporarily hide one entry, click Hide on its line. To hide
all entries click Hide all, to toggle which entries are hidden
click Toggle.
To delete an entry, click Delete.
10.0 Credits
The following are in no particular order but all are greatly
appreciated:
Thanks to Lutz Mandle for restoring SOHO support in 2012; showing sun in
moonview; proxy support in web downloads; improved horizon clipping and
correct use of Sky View options in individual planetary views.
Enormous advances in data quality were
contributed by the late Guillermo Andrade Velasco.
The Blue Marble project at
http://earthobservatory.nasa.gov/Newsroom/BlueMarble
for their
wonderful
whole-earth color images.
Corrections for ecliptic longitude from Adrian Robinson<EMAIL_ADDRESS>The stellar spectra colors are based on work by Mitchell Charity,
<EMAIL_ADDRESS>at
http://www.vendian.org/mncharity/dir3/starcolor.
Thanks to Paul Schlyter for some improved anomaly code.
Dean Huxley contributed improved constellation figures and improved
the Tycho Hipparcos data base.
Thanks to Thomas Conze<EMAIL_ADDRESS>for several great
patches.
Thanks to Matei Conovici<EMAIL_ADDRESS>for making Sky View's "live
report" option a saveable preference.
Several nice tweaks and some thorough debugging from John O'Donnell,
<EMAIL_ADDRESS>Thanks to Jean-loup Gailly and Mark Adler for zlib.
Thanks to Eric S. Raymond for his fine implementation of base64.
Milky Way contour by Pertti Paakkonen<EMAIL_ADDRESS>in
turn
based on map from http://www.ebicom.net/~rsf1/fun/sm-new.htm copyright
(c)
1972,2001, R.S. Fritzius, may be reproduced for non-commercial purpose.
The local magnetic declination model is from the DoD World Magnetic
Model as published at http://www.ngdc.noaa.gov/seg/potfld/DoDWMM.shtml
Thanks to Fridger Schrempp<EMAIL_ADDRESS>for his long
term encouragement of the project, and particularly for many
suggestions
to improve ease of use.
Thanks to Wolfgang Steinicke of www.ngcic.org for allowing use of
his corrected NGC and IC catalogs.
Earth satellite orbit propagation is based on the NORAD SGP4/SDP4
code, as converted from FORTRAN to C by Magnus Backstrom,
<EMAIL_ADDRESS>See "Spacetrack Report Number 3: Models for
Propagation of NORAD Element Sets" at
http://www.celestrak.com/NORAD/documentation/spacetrk.pdf
Improvements to Delta T code, help and wording contributed by Neal
McBurnett<EMAIL_ADDRESS>Any parts of the USNO SA2.0 catalog that are included with XEphem
distributions are done so with the following understandings:
It may not be the latest version, check with http://ad.usno.navy.mil
If you paid for XEphem, you paid for the software, not this
catalog. The catalog is available free from the USNO.
Inclusion of the SA2.0 catalog does not imply an endorsement of
XEphem by USNO; nor did I have privileged access to the catalog; nor
does the US Government affirm or guarantee that XEphem works
properly in any way.
Thanks to Atsuo Ohki<EMAIL_ADDRESS>for numerous
fixes and features.
Thanks to Robert Lane<EMAIL_ADDRESS>for Uranonmetria 2000
work.
Martian relief map completed June 2000 using data from Mars Orbiter
Laser
Altimeter on board the Mars Global Surveyor, operated by the Jet
Propulsion
Laboratory, NASA.
See http://marsprogram.jpl.nasa.gov/mgs
The near real-time weather map in the Earth view is provided by
the Space Science and Engineering Center at the University of
Wisconsin.
See their web site at http://www.ssec.wisc.edu/ssec.html
The XEphem logo was contributed by Jonathan Adams,
<EMAIL_ADDRESS>The galaxy background image is from Galaxy
Photography, www.galaxyphoto.com.
For the years 1999-2010 the natural satellite ephemerides for Mars,
Jupiter, Saturn and Uranus are based on developments in mixed
functions computed and contributed at Bureau Des Longitudes,
http://www.bdl.fr
by J.-E. Arlot, Ch. Ruatti and W. Thuillot. Many
thanks!
Outside this range, Jupiter's moons based on information in
"Astronomical Formulae for Calculators" by Jean Meeus. Richmond, Va.,
U.S.A., Willmann-Bell, (c) 1982. Saturn's moons based on code and
ideas supplied by Dan Bruton, Texas A&M<EMAIL_ADDRESS>For all
dates, ring tilts based on "RINGS OF SATURN" program by Olson, et al,
Sky & Telescope, May 1995, page 95. C code as converted from BASIC
by<EMAIL_ADDRESS>(Paul Martz).
Thanks to Monty Brandenberg<EMAIL_ADDRESS>for his
assistance and solution to the unaligned access messages on Digital
UNIX.
Thanks to Christophe Magneville<EMAIL_ADDRESS>for finding
an array subscript and a numeric overflow problem in libastro.
Thanks to Jean-Etienne Lamiaud for a fix to
prevent gif color tables from hogging more than their share of X
colormap entries, many corrections to xephem_sites, and a nice speedup
to
Sky View depth sorting.
Thanks to Egil Kvaleberg<EMAIL_ADDRESS>for key idea on how to
support 8 bit FITS images.
Thanks to Stuart Levy<EMAIL_ADDRESS>for his work converting
the Tycho ESA mission database
adc.gsfc.nasa.gov:/pub/adc/archives/catalogs/1/1239 into xe format.
Images of Saturn from STScI.
Many formulas and tables are based, with permission, on material
found in: "Astronomy with your Personal Computer" by Dr. Peter
Duffett-Smith, Cambridge University Press, (c) 1985.
The high precision planet positions were implemented for XEphem by
Michael Sternberg<EMAIL_ADDRESS>based on the
papers
- "Planetary Theories in rectangular and spherical variables:
VSOP87 solution" by Bretagnon P., Francou G., in Astron. Astrophys.
202, 309 (1988), ftp://ftp.bdl.fr/pub/ephem/planets/vsop87/, and
- "Representation of planetary ephemerides by frequency analysis.
Application to the five outer planets" by Chapront J., Astron.
Astrophys. Suppl. Ser. 109, 181 (1995), ftp://adc.gsfc.nasa.gov/\
pub/adc/archives/journal_tables/A+AS/109/181.
See the comments in chap25.h and vsop87.h for accuracy estimates.
The high precision Moon code was also implemented for XEphem by
Mr. Sternberg based on code supplied by Stephen L. Moshier
<EMAIL_ADDRESS>at
ftp://ftp.std.com/pub/astronomy/selenog.zip. Mr. Sternberg also
incorporated the algorithm for deltaT, based on code also provided by
Mr. Moshier. See the comments in deltat.c for full references. My
greatest thanks to Messrs. Sternberg and Moshier for their generous
and kind assistance in making XEphem a program of first-class accuracy.
The improved lunar libration trig series fit to JPL DE403 was
provided by Stephen L. Moshier<EMAIL_ADDRESS>Many thanks to Michael Naumann<EMAIL_ADDRESS>and Miguel
Albrecht<EMAIL_ADDRESS>at ESO and Tim Kimball<EMAIL_ADDRESS>at STScI for their help and support accessing the DSS at their
institutions. And thanks to ESO and STScI in general for offering this
service at all.
Thanks to Seiichi Yoshida<EMAIL_ADDRESS>for
a subtle fix to the constellation code in 3.1.
The sample spacecraft elements were furnished by Ron Baalke,
<EMAIL_ADDRESS>Thanks to Vance Haemmerle<EMAIL_ADDRESS>for his
updated and appended lists of spacecraft elements, and work on
improvements to the solar system plotting of long-period trail
sequences.
Thanks to Jeroen Valkonet<EMAIL_ADDRESS>for planting the seed
which grew into the new bitmap clipmask approach of drawing the stars.
Thanks to Jim Bell<EMAIL_ADDRESS>and the team at
Mars Watch for encourage, support and ideas for the first Mars albedo
map in XEphem. The map as of Version 3.3 is from
http://maps.jpl.nasa.gov/mars.html
Thanks to Dimitromanolakis Apostolos<EMAIL_ADDRESS>for
his contribution leading to support for fetching DSS in gzipped form.
Thanks to Miguel Albrecht<EMAIL_ADDRESS>at ESO for
his assistance and support of their fine Web access facilities to the
GSC.
Rotated trail text uses the xvertext package. Here is the copyright:
xvertext 5.0, Copyright (c) 1993 Alan Richardson
<EMAIL_ADDRESS>Permission to use, copy, modify, and distribute this software
and its documentation for any purpose and without fee is hereby
granted, provided that the above copyright notice appear in all
copies and that both the copyright notice and this permission notice
appear in supporting documentation. All work developed as a
consequence of the use of this program should duly acknowledge such
use. No representations are made about the suitability of this
software for any purpose. It is provided "as is" without express or
implied warranty.
IC.edb was submitted by Christos Siopis<EMAIL_ADDRESS>Constellation algorithm is from a paper by Nancy G. Roman,
"Identification of a constellation from a position", Publications of
the Astronomical Society of the Pacific, Vol. 99, p. 695-699, July
1987. Before 3.6 the figures were the work of Chris Marriot. The list
of
boundaries is derived from the three files constell.1875.data,
constell.1875.hdr and constell.doc at
ftp://explorer.arc.nasa.gov/pub/SPACE/FAQ/.
The WCS solver algorithm technique was inspired by a paper by Frank
Valdes in PASP, vol 107, page 1119 (1995).
New version of Gemini constellation by Lutz Maendle,
<EMAIL_ADDRESS>Thanks to Dr. Harald Fischer<EMAIL_ADDRESS>for the GPS
awk routine and sample position database.
The high-precision precession routine is from 1989 Astronomical
Almanac, as interpreted by Craig Counterman. Mr. Counterman also
deserves the credit for providing the initial encouragement to write
an astronomical tool specifically for X Windows back in 1990, and for
significant assistance while developing the heliocentric models.
The Earth map is derived from data supplied with xearth which
included the following notice:
Copyright (C) 1989, 1990, 1993, 1994 Kirk Lauritz Johnson
Permission to use, copy, modify, distribute, and sell this
software and its documentation for any purpose is hereby granted
without fee, provided that the above copyright notice appear in all
copies and that both that copyright notice and this permission
notice appear in supporting documentation. The author makes no
representations about the suitability of this software for any
purpose. It is provided "as is" without express or implied warranty.

The Earth shaded elevation relief map shipped with XEphem 3.6 is
from the
National Geophysical
Data Center. The one with 3.7.6 is from
http://www.shadedrelief.com/world_relief/download.html
The pulsar and Radio databases are based on lists supplied by Robert
Payne<EMAIL_ADDRESS>Errors in converting to XEphem are mine.
The lunar image is based on one I found surfing at:
ftp://seds.lpl.arizona.edu /pub/images/planets/moon/fullmoon.gif. The
calculations for the longitude of the terminator and the solar
altitude are based on the program colong.bas by David Bruning and
Richard Talcott, published in _Astronomy_, October 1995, page 76.
Thanks to Richard Clark<EMAIL_ADDRESS>for an improved
version of anomaly.c.
A great source of comet information is http://encke.jpl.nasa.gov
Special thanks to Uwe Bonnes<EMAIL_ADDRESS>and Ralphe Neill<EMAIL_ADDRESS>for their many ideas and
support.
Many test cases were gleaned from the pages of Sky and Telescope,
(C) Sky Publishing Corp.
Many of the sample cities in the "xephem_sites" file are from the
xsat program, which included the following notice:
Copyright 1992 by David A. Curry
Permission to use, copy, modify, distribute, and sell this
software and its documentation for any purpose is hereby granted
without fee, provided that the above copyright notice appear in all
copies and that both that copyright notice and this permission
notice appear in supporting documentation. The author makes no