XEphem is an astronomy program X11/Motif for Linux, Mac OS X and other Unix- like operating systems. It is proprietary software whose source code for personal use, however, is available. Through the use of VSOP87 XEphem reached a very high accuracy in the calculation of the ephemeris, the current planet positions. This also explains the name XEphem: Ephemeris under the X Window System.
- 2.1 orbital elements
- 2.2 Field Stars
The continuously developed since 1993 the program has a very wide range of functions, which is clearly focused on the needs of the observing star friend. Key elements thereof are to be outlined in the following.
XEphem can first and foremost a current, ie, time-and location-based, Star Chart ( XEphem: sky view ) to create, which can contain the respective positions of planets, asteroids, comets and satellites. This detail or zoom factor and the objects to be displayed can be selected by type and also by brightness. Detailed maps with high or maximum zoom factor can be highlighted via the internet with images of the Digitized Sky Survey.
Already ephem the program under which the X11 program XEphem emerged, ephemeris could ( XEphem: dataTable ), so the current positions of the planets calculate. The Ephemeridentabelle XEphem can be extended both to numerous, can be derived from the coordinates of sizes as well as to other, defined through catalogs or web members objects of the solar system.
Also a model-like look at the ecliptic, the common plane in which the planets orbit around the sun is possible. Again, further objects of the solar system can be integrated; to choosing among dataIndex an object and stores it as a favorite. The resulting three-dimensional model of our solar system can be viewed from different directions.
The erdzugewandte side of the moon is an interactive Moon Atlas are available. On request, moon near the fixed stars and planets are shown, so that can also simulate lunar occultations.
Jupiter, its four Galilean moons and their shadows can also be displayed in the current situation. Also, the Great Red Spot, a very stable cyclone system of Juptieratmosphäre is detected. Since the geographical longitude of the Great Red Spot is subject to certain fluctuations, the length of the spot can be set manually.
Similar functionality is also available for the planets Saturn and Uranus.
The Earth may be represented both as a ball as well as a cylindrical projection. In an animation can be observed the daily and seasonal movements of the sun-lit hemisphere. Phenomena as the midnight sun near the poles and questions concerning the shift of sunrise and sunset times are well understood here. The core shadow zone during a solar eclipse will be calculated and displayed here.
About Internet will change the current global weather situation can be represented.
Moving images can be produced with a constant time interval as a sequence of frames. In some firmer view (such as in earth view and the solar system view) There do its own menu item animation demo. The animation of the day - night boundary was produced by XEphem. In reality, the transition from day to night is geometrically course not as sharp-edged limited, as the graph suggests it. It is, rather, a few hundred kilometers wide strip. At sunset, the Earth's atmosphere acts like a lens and delayed these seemingly. This effect, which relates to the same horizon also nearby stars is taken into account by XEphem when creating a star map in the horizon system by the way. Serve for this purpose to the location above sea level and the actual temperature in the main window.
The time interval between two images in the adjacent animation is 14 days plus or minus of the time to local sunset. The individual images were created in the earth view and added a XEphem movie. By storing a sequence of PNG files, with the netpbm tools (see Netpbm (English ) ) was converted into GIF format and was put together with gifslice to a GIF animation.
In addition, orbits of planets and other portable objects as so-called trails, as a kind of tracer that seem to lambast these objects behind you generate. In this way, the Mars loop was generated in the screenshot shown above right.
Making such trails usually only when using the Equatorial coordinate system sense. When using the azimuthal coordinate system XEphem warns the user in accordance with bewildering star maps.
Time series and graphs
The Chance, XEphem a sequence of snapshots to let each generate in the same time interval, can be used both for creating time series with output to a text file (list values under Tools ) and for graphical representation astronomical sizes and their dependencies (plot values).
The XEphem program itself has only a few hard-coded objects: the planets and their major moons. All other celestial bodies are defined in the so-called catalogs (see star catalog ), which can be loaded and unloaded at runtime. XEphem used here own a text format that is usually the file extension. Edb used. The most important of these catalogs are included with the source code XEphem - via the website XEphem available CD version has a significantly extended range of such catalogs. Often provide astronomical catalogs Institute for XEphem on the Internet for download.
The only over short periods of time useful orbital elements of asteroids, comets and satellites can even be easily updated via the internet directly into XEphem ( menu item Data Download ) by the relevant institutions ( Minor Planet Center at Harvard University, the International Astronomical Union, Lowell Observatory ).
The default XEphem used fixed star catalog contains SKY2k65.edb good eight thousand fixed stars to about 7 mag. This roughly corresponds to those stars that can be seen under favorable viewing conditions with the naked eye (about 6.5 mag ). Even with a powerful pair of binoculars but can also significantly smaller stars, until about 10 mag, watching.
To illustrate the quite large number of such faint stars XEphem has a sophisticated mechanism: the so-called field stars. Namely, there is no need to load all these stars into memory. For a meaningful way should these stars are shown only at a correspondingly high zoom factor and thus a small image. This is exactly what happened: In a large zoom factor of a special catalog ( in a binary format, as a so-called quadtree is used) exactly the required size for each section of the sky faint star charged.