xephem(1X)

Name
xephem - an interactive astronomical ephemeris for X

Syntax
xephem

Description

XEphem version 3.2 is an interactive astronomical ephemeris program for X Windows systems with Motif. It provides many graphical views as well as quantitative heliocentric, geocentric and topocentric information for Earth satellites, solar system and celestial objects.

Getting Started

XEphem contains extensive context-sensitive on-line help. Virtually none of that help is duplicated here so go ahead and run xephem to learn more. When you first run xephem you may hear a beep. This means xephem has added a message to the message box menu. This menu is not shown by default. Whether the message box is displayed may be toggled by using the Messages entry in the File pulldown menu off the Main menu. Whether xephem beeps when it adds a message may be toggled using the Message Bell option in the Preferences pulldown menu.

Quick Menu Tour

The Help pulldown at the top right of the main menu provides access to several categories of assistance applicable to the overall operation of xephem. Those unfamiliar with xephem might begin by reading the Introduction help section first and reading the additional help information in the order in which it is listed in the pulldown. In particular, Examples leads to several useful practice operations. The Main menu of xephem provides control and display of three basic services: observing circumstances, looping, and access to additional displays. Observing circumstances includes location, time and atmospheric conditions (used for the refraction model). Looping refers to the ability to set up xephem so that it automatically increments time at a desired step size and rate. Additional displays provide all of the graphical and quantitative information available, and always refer to the circumstances defined in the main menu. These additional displays are activated from the Views pulldown. XEphem has information about the Solar system built in which can be accessed without the need to access an external database. But XEphem can read files of additional objects into memory as well. Files of objects are read in using the Load and Delete button in the Objects pulldown. The definition of any object in memory may be inspected and manipulated in detail and assigned to so-called `user defined objects' X, Y and Z using the Search and ObjXYZ button in the same pulldown. All of the data that xephem presents in numeric form may be written to a file and later plotted; written to a file as a tabular listing; or used to formulate an arbitrary mathematical expression that may be solved for a maximum, minimum or zero. These facilities are accessed from the Control pulldown. Several general computational and display options may be controlled from the Preferences pulldown. The Files pulldown allows one to reset the main menu to the initial resource settings; toggle whether the general messages box is displayed; and quit the program.

X Resources

XEphem has many X resources, some of which you will soon want to tune to your taste and circumstances; many others may be left unchanged. Look through the XEphem.ad sample in the distribution for full details. If no resources are available, xephem contains reasonable internal fallback resources. Of course, in addition to all the custom resources, xephem supports the usual Xt command line arguments such as -display, -xrm, -synchronous, -fg and -bg. xephem may install a private colormap when it first starts if it finds few color cells available. This can also be forced from the command line using the -install option. This option should be followed by one of the following keywords: guess, yes or no. The application class of xephem is XEphem. You may get a list of all the builtin fallback resources by using the -prfb option.

Time zones
xephem will attempt to support time zone control information from the host operating system. If this fails for some reason, time zone offset and name may always be set manually at any time from the Main menu, or they may be initialized from the XEphem.TZName and XEphem.TZone resources, respectively.

Author

Elwood Downey, email ecdowney@ClearSkyInstitute.com.

References

The latest information about xephem is maintained at http://iraf.noao.edu/~ecdowney/xephem.html. (Although they graciously host the distribution, xephem is not associated with the National Optical Astronomical Observatory.)

The online Help entry on Credits lists many of the references, individuals and organizations which have contributed to xephem, to all of which I am most grateful.