UNITS

The units of the SIZEn columns. The options are listed in Table . The size of the symbol may be specified as an absolute angular size, in which case the units will usually be one of the angular measures. Here the size of the symbol corresponds to the actual size of an extended object on the sky. For example, the size of a circle could correspond to a circular isophote for a nebula. The `fraction' option is provided for the other case where the symbol size varies with some property of the object, such as magnitude, which is not an actual angular extent on the sky. Here the symbol size is simply a fraction of the $x$ axis range of the plot (expressed on a scale where the entire range corresponds to 1.0). If omitted the default is fraction.

Table: Plotting UNITS

Description	Name
fraction of $x$ range	fraction
seconds of arc	arcsec
minutes of arc	arcmin
degrees	degrees
hours	hours
radians	radians