The results of most commands of ASTRO depend on the observer's
location on Earth. This information is input to the software using the
OBSERVATORY longitude latitude altitude [sunlimit]
where the longitude and latitude are in degrees (with the usual
convention of positive values towards North and East respectively) and
the altitude is in kilometers. The fourth parameter is the radius of
the sun avoidance circle (default is 30 degrees), used to indicate in
plots the sky area that cannot be observed. A number of
observatories are pre-defined and can be selected directly by typing:
Known observatories are given in Table . Note, that the Plateau de Bure sun avoidance limit used to be 45 degrees, but has been decreased to 35 degrees in July 2009. For the submillimeter and millimeter facilities within this list, ASTRO also assumes an antenna diameter, that is used to compute the beam size and thereby the main beam brightness temperatures of planets (see PLANET command).
When entering only OBSERVATORY (without argument), ASTRO will select the default observatory. The latter is defined by the GAG_ASTRO_OBS logical:
SIC LOG GAG_ASTRO_OBS PICO ! define PICO as default observatory OBSERVATORY ALMA ! select ALMA as observatory OBSERVATORY ! select PICO as observatory
For IRAM instruments and ALMA, the observatory selection activates commands to prepare receiver and correlator setups (see related chapters). In this frame, the commands OBSERVATORY NOEMA and OBSERVATORY PDBI (or BURE) select the same position on Earth, sun limit and dish diameter, but different commands to represent the different hardware status (PDBI/BURE = up to 2017, NOEMA = as of 2017).
Note that some commands take into account different versions of the hardware. They are accessible by adding an argument after the observatory name. For PDBI and NOEMA, versions are identified through years. For ALMA, versions are identified by cycle number.
Note for experts - The logical GAG_ASTRO_OBS is defined in the gag.dico.gbl file in the GILDAS distribution. By default, it is set to BURE. To override this default, users have to "export GAG_OBSERVATORY=ObservatoryName" just before sourcing gildas-env.sh at the beginning of the compilation procedure. Another possibility to permanently modify the value of GAG_ASTRO_OBS is to edit the astro-site.astro procedure (see section ).