AstroGrav Help /Menus /Tools /Generate EphemerisVersion 4.5
Tools / Generate Ephemeris ()Operating Systems: All
Window Types: All
Simulation Types: Solar system only
Generates an ephemeris for an object in the frontmost simulation while it is evolving.
When you select this command, a new ephemeris window will be opened in the frontmost simulation. If there was an object selected in the original window, then the new ephemeris window will automatically default to this object. If there was no object selected in the original window, then the new ephemeris window will show an input dialog in which you can type the name of the object whose ephemeris you want to generate. This input dialog and its behaviour are identical to the input dialog displayed when you use the Edit / Find... command.
The ephemeris window contains the following components.
- A View From... button that allows you to choose a viewing location for the ephemeris. When you click on this button, the AstroGrav locations dialog will be displayed. This is the same dialog that is displayed with the Tools / Edit Locations... command.
- The chosen viewpoint, which is displayed as a country, town, latitude, longitude, and altitude.
- The ephemeris table, which occupies most of the ephemeris window and initially shows a default set of columns. Several other possible columns are available, and you can use the column selector () icon in the top-left corner of the table to show these hidden columns or to hide unwanted columns in the default set. The full set of available columns is as follows.
- Epoch - the epoch in local time
- Right Ascension - the right ascension of the target object in hours : minutes : seconds
- Declination - the declination of the target object in hours : minutes : seconds
- RA Proper Motion - the right ascension component of the proper motion in arcseconds per minute
- Dec Proper Motion - the declination component of the proper motion in arcseconds per minute
- Total Proper Motion - the total proper motion in arcseconds per minute
- Position Angle - the proper motion position angle in degrees
- Azimuth - the azimuth of the target object in degrees
- Altitude - the altitude of the target object in degrees
- Azimuth Motion - the azimuth component of the azimuth/altitude motion in arcseconds per minute
- Altitude Motion - the altitude component of the azimuth/altitude motion in arcseconds per minute
- Total Motion - the total azimuth/altitude motion in arcseconds per minute
- Position Angle - the azimuth/altitude motion position angle in degrees
- Distance - the distance between the target object and the viewpoint in astronomical units
- Separation - the distance between the Sun and the target object in astronomical units
- Elongation - the angle between the Sun and the target object (subtended at the viewpoint) in degrees
- Phase - the phase of the target object in the range [0, 1]
- Phase Angle - the angle between the Sun and the viewpoint (subtended at the target object) in degrees
- Magnitude - the magnitude of the target object
- Radial Speed - the radial speed of the target object in kilometers per second
- Transverse Speed - the transverse speed of the target object in kilometers per second
- Total Speed - the total speed of the target object in kilometers per second
An export () icon in the bottom-left corner of the table allows you to export the ephemeris data in a form that is easily imported into a spreadsheet application such as Microsoft Excel. When you click on this button, a file chooser dialog will be displayed that allows you to navigate your computer's file system to choose a location and name for the exported file. The exported file will be a text file that can be viewed in a text editor, word processor, or spreadsheet application, although because the exported data is effectively tabular, a spreadsheet application is the most appropriate. When an exported ephemeris is viewed in a spreadsheet application, there will be one column for each column of the ephemeris table and one row for each time in the ephemeris, so that the exported data is presented in a similar form to when it is viewed in AstroGrav.
- A Planetary Aberration checkbox that allows you to choose between an ephemeris of the selected object as it actually is, or an ephemeris of the selected object as it appears to be, taking into account stellar aberration, diurnal aberration, and light-time correction.
- A Refraction checkbox that allows you to choose between an ephemeris in which refraction is excluded, or an ephemeris in which refraction is included. If refraction is included, figures near the horizon can be inaccurate due to varying local atmospheric conditions that AstroGrav is unable to take into consideration.
- A Use JNow checkbox that allows you to choose between an ephemeris in which the J2000 reference frame is used for the equatorial coordinates, or an ephemeris in which the JNow reference frame is used for the equatorial coordinates.
- A Clear button that allows you to clear the contents of the ephemeris table.
Having chosen the required target object and viewpoint, you then use one of the commands in the Evolve menu to run the simulation and generate the ephemeris. You get one row of the ephemeris for each time step, so you might first want to use the Evolve / Settings... command to change the time step.
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