Ephemeris Windows

Introduction

Ephemeris windows let you view a simulation in the form of a table with ephemeris data in the columns, and with each object's data occupying one row of the table. Objects can be selected to generate ephemerides for them.

You can open a new ephemeris window by using the Window / New Ephemeris command, or by using the Window / Duplicate command on an existing ephemeris window.

Generating Ephemerides

Each 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 chooser, which occupies most of the ephemeris window, and which shows each object's data occupying one row of the table, with 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.
  • Name - the name of the object
  • 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 table is viewed in a spreadsheet application, there will be one row of the spreadsheet for each row of the table and one column of the spreadsheet for each column of the table, 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 object data as it actually is, or object data 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 object data in which refraction is excluded, or object data 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 object data in which the J2000 reference frame is used for the equatorial coordinates, or object data in which the JNow reference frame is used for the equatorial coordinates.

• A Generate button that allows you to generate an ephemeris for the selected object.

Having chosen an object and clicked on the Generate button, a new tab will be added, which shows an ephemeris table for that particular object. This table is similar to the ephemeris chooser, but with the following differences.

• The Name column is replaced with the Epoch column.

• Each row of the table shows a particular epoch of the ephemeris, instead of a particular object in the simulation.

• The Generate button is replaced with the Clear and Remove buttons, which allow you to clear the contents of the ephemeris table, or to remove it completely.

When first created, an ephemeris table has just one row, which shows the object's data for the current epoch. You can then use one of the commands in the Evolve menu to run the simulation and generate the ephemeris. You get one row of an ephemeris for each time step, so you might first want to use the Evolve / Settings... command to change the time step.

The ephemeris chooser's Generate button can be used multiple times to generate multiple ephemerides in one ephemeris window, with each object's ephemeris becoming visible when its particular tab is selected.

Copyright © 2005-2024, AstroGrav Astronomy Software