Keywords: astro

Next: Solar system bodies Up: Computing source positions Previous: Source catalogs Contents

## Source selection

Once a catalog has been defined, a source within this list can be selected using the `SOURCE name` command. The `/ALTERNATE` option will direct the search to the alternate catalog.

The source coordinates are reduced to current epoch (as defined by the last `TIME` command), and converted to horizontal coordinates azimuth and elevation relative to the observatory (as defined by the last `OBSERVATORY` command). Precession, nutation, aberration are taken into account. The motion of the Earth uses the ephemerides from the Bureau des Longitudes (BDL82). The source horizontal coordinates are printed on the screen, together with the line-of-sight components of the velocities of:

- the source relative to the observer (S/OBS)
- the source relative to the standard of rest (S/LSR)
- the standard of rest relative to the Solar System barycenter (LSR/G)
- and the Solar System barycenter relative to the observer (G/OBS)

All velocities are in km/s, counted positively for outwards motions. After running the `SOURCE` command, a number of `SIC` gloabal variables are updated and contain the source right ascension (variable `RA`), declination (`DEC`), azimuth (`AZIMUTH`) or elevation (`ELEVATION`). These are global `ASTRO` variables, used or mnodified by other commands. In addition, a structure called `astro%source%` is created, and contains all output values of the `SOURCE` command.

`SOURCE` with no arguments will compute positions of all sources from the current (or alternate) catalog in a row. The `SIC` variables will contain the position of the last source.

SOURCE /RESET will reset all source related parameters in ASTRO and remove the ASTRO%SOURCE structure.

Next: Solar system bodies Up: Computing source positions Previous: Source catalogs Contents