# 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