Keywords: astro

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# Observability bar charts

Figure: Plotting an observability chart.

A extremely convenient mean of planning observations is to produce a diagram in which time is used as x-coordinate, and in which an horizontal bar is drawn for each selected source to indicate the time period during which the source is up. Such a plot is produced using the command `HORIZON`. One may use all sources in the current catalog (`HORIZON /SOURCE`), all planets (`HORIZON /PLANET`), or both. Specific objects may be called by their names using `HORIZON /SOURCE name1 name2 ...` or `HORIZON /PLANET name1 name2 ...`. A source that is presently in the sun avoidance circle is written within brackets ([]) and in italics (e.g. [NGC 2264]). When a quite long catalog is used, the command `HORIZON /SOURCE NEXT n` can be used repetitively to obtain plots with only `n` objects at a time.

Example - The following commands will plot the observability hours for the sources of the `sample.sou` catalog on April 1st 2008, together with planet Neptun. The output is presented in Fig. .

      CATALOG GAG_DEMO:SAMPLE.SOU         ! define the catalog
      OBSERVATORY PICOVELETA              ! ... the observatory
      TIME 12:00 01-APR-2008              ! ... and the time
      HORIZON /SOURCE /PLANET NEPTUN      ! produce the plot

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