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Go to https://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]. Note that geocentric locations should no longer be used.
- Time Span should be set as needed. The ephemeris should contain at least one row for every hour and, except for fast objects, one row every 20 minutes is sufficient. The online system will linearly interpolate between rows in an ephemeris when determining the antenna pointing and propagation delay.
- 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. It is also recommended that ``extra precision'' be selected from the optional settings. Do not select the elevation cutoff option as this is likely to fail.
- 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, 2018 Sep 25