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Go to http://ssd.jpl.nasa.gov/horizons.cgi. The HORIZONS web interface shows the current settings, all of which can be modified using the ``change'' link. Previously-used settings seem to be remembered, so we first recommend that all inputs should be set to their default using the ``Special Options'' section. The inputs should then be set as follows:
- Ephemeris Type should be ``Observer'' (default).
- Set Target Body to the relevant solar-system body.
- The Observer Location is most easily set to ALMA using the ``Lookup named location'' interface (the HORIZONS numerical code for ALMA is -7). These instructions have recently (Feb 2013) changed - geocentric locations should no longer be used!
- Time Span should be set as needed. To ensure sufficient accuracy, we recommend that entries every 10 minutes are requested. However, in general, more frequenct sampling should be avoided due to file size limits. Files with up to 90000 rows have been successfully tested.
- Of the many possible Table Settings, only ``Astrometric RA & DEC'' (1) and ``Obsrv range & rng rate'' (20) are required. Do not select any of the optional settings as none have been tested with ALMA. It is known, however, that ``extra precision'' and ``elevation cutoff'' do not work.
- Display/Output should be set to ``plain text''.
Once the inputs have been checked and found to be okay, the ephemeris can be generated. This will take the form of text in the browser window which should be saved to a text file. This can then be read into the Science Goal or SB.
Next: Example Ephemeris
Up: Create an External Ephemeris
Previous: NASA resources for HORIZONS
Contents
The ALMA OT Team, 2013 Feb 27