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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. Entering ``ALMA'' will enable a search and the entry that should be chosen is Atacama Large mm/sub-mm Array (ALMA) Center of Array [-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 during the observations, sampling at 10-minute intervals is recommended. More frequent sampling should be avoided due to file size limits, although files with up to 90000 rows have been successfully tested.
- Of the many possible Table Settings, only Astrometric RA & DEC and Obsrv range & rng rate are required. If correctly chosen, the interface should read QUANTITIES=1,20. 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, 2014 May 21