Xephem -- Small On Requirement, Big On Features
Xephem is a free planetarium program for Unix and Linux that can be obtained
from The Clear
Sky Institute. While the Sky View display isn't up to esthetic appearance
of Kstars or especially Stellarium, it is a highly functional and configurable
planetarium program. And -- it is much more bug free.
This web page gives an overview of some of the features of Xephem. I
invite you to check out Tonight's Sky, which uses a number of Xephem displays to present what the sky is
Use this custom search engine to shop for other astronomy software (try planetarium software):
Xephem has many types of displays, not just the general Sky View star
screen, an example of which is shown below:
Xephem Star Screen Shot Segment
In the screen shot example, you can see a number of green symbols, some
labeled. These are Messier, Caldwell, and Hershel 400 objects. Xephem
allows you to determine how many are automatically labeled, and right
clicking on any one of them will show the label, location, type, and other
It's worth noting that while the Messier objects were already in the
Xephem database, I was able to add the Caldwell and Hershel objects by
following Xephem documentation.
Some of the Main Features
Xephem allows the user to enter a location for which to present the
night sky. When Xephem comes up, it automatically sets the time for the current
time, but the user can select any other time, or simply click a button to
advance or retard the display by a selectable time step.
On the star map, holding down the center mouse button will allow you to
move the star map to a desired section. One can also use a scroll bar at the
bottom of the display to move in azimuth, and a vertical scroll bar at the
right of the display to move in elevation. A vertical scroll bar at the left
of the display zooms the map in and out.
Many features on the display can be set either from an options pull down
or from buttons across the top of the display. One can turn on or off the
horizon line, constellation lines, object labels, grid lines, solar system
objects, and deep space objects. When exiting, the user is given the option
to save the current settings of all options.
The star magnitude limit for displaying stars and nebulae can be selected.
From the basic control window, object catalogs can be selectively turned off
See the Orientation of Planets and Moon for Any Time
Xephem has views for the Moon, Jupiter, Saturn, and Mars, showing their
view from the selected Earth location and time. Each of these displays, when
selected, pop up as a separate window. The moon image, shown below, shows the
current lunar phase and a long list of lunar features than can be selected,
which places their label on the moon map. The moon map can be zoomed in
and out for an appropriate display.
Xephem Moon Map
An example of the planet views is this Xephem Jupiter view. It shows the
planet, the location of the Galilean moons, and the great red spot for any
selected time. A great tool for planning your Jupiter observing sessions. The
image can be flipped to accommodate any orientation provide by your
telescope view, and zoomed in or out to adjust the field of view.
Xephem Jupiter View
Similar views, helpful for planning planetary viewing sessions, are
available for Saturn and its moons, and Mars with it's features.
One of My Favorites -- Favorites!
Xephem has a feature called favorites. It comes pre-loaded with the Sun,
Moon, and planets. Clicking on favorites will drop down the favorites menu, and
selecting an object will cause the night sky (star) window to place a reticle
over the desired object. If the object is not currently in the window view, the
window view is moved to place the object in view.
This is really handy for finding the planets, but I've found that it can
be much more than that. You can right-click on any object and the pop up
info for that object will let you add it to favorites. You can also use the
options menu to select different favorites lists.
I enjoy looking at double stars, but often forget exactly where some of them
are. I've found some double star listings appropriate for my telescope, found
these on the map, and added them to a new favorites I call doubles. Now I can
click the favorites button to get the pull down, and click any double in the
list to have Xephem show me where it is. Quite handy.
Other Features and Final Thoughts
Xephem has many other features, some probably a bit arcane for the
average amateur astronomer. For example under the tools menu, one has
some mathematical utilities for solving astronomical equations and plotting
There's a preference menu for setting display colors, precisions, and other
features. There's a data menu where you can enter new object lists you prepare,
as described in the Xephem help information. On the data/files menu you
can select to turn on or off any of the catalogs you've added.
On the Sky View display, the options menu provides an eyepiece function
where one can set up different viewing fields of view. Then any of these
field of view setups can be selected. Then on the star map, one can right
click on a region of the display and select Place Eyepiece. This
causes a circle of the selected field of view to appear on the display.
Right clicking again gives the option to delete the eyepiece circle. This
is a handy option particular for planning use of wide field instruments,
such as binoculars.
In the example below, the area of M31 is zoomed in, and a field of view
defined for my binoculars is shown superimposed on M31 (the red circle). As
you can see by this display, M31 is a pretty spectecular object even in a
pair of binoculars, nearly spanning the entire field of view.
Xephem Eyepiece Feature
Be sure to check out many contributed features available at the
The Clear Sky Institute. If you examine their library, you'll find that Xephem is one of the
most capable PC planetarium programs available.
I've used Kstars, Stellarium, and Xephem for some time. Each has its
handy features. Kstars is nice for it's display and the ability to associate
web page links to any object. Stellarium gives the most realistic display,
though it requires a 3D card to do so. Xephem gives the most basic display,
but is the most responsive. It can run on the smallest computer. It also
is the only one of the three that let me add my own object catalogs and
display them properly.
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