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The units named in the IAU (1988) Style Guide
are recommended for array and keyword values, with the exception of measurements
of angles. This set of units includes the SI units and additional units that are
standard in astronomy, for example, magnitudes. Using BUNIT and TUNITn
keywords will remove any confusion; similarly, the comment field following CTYPEn
keywords can be used to specify the units. Fractional units should not be used.
If, for example, for space reasons, temperatures must be listed in the file in
units of tens of degrees, the units specified by BUNIT should be degrees,
and scaling (section 3.1.2.1) should
be used to transform from the file values to physical values. Always explicitly
describe non-standard units. A copy of the IAU Style Guide recommendations is
available on the IAU World Wide Web site, currently at
http://www.iau.org/units.html.
For celestial coordinate systems specified with the CTYPEn,
CRVALn, CDELTn, and CROTAn
keywords, or with the keywords used in the world coordinates conventions described
in section 4, the use of decimal degrees for
the angular measurements is required, and degrees are recommended as the units
for other angular measurements (with, for example, the value of BUNIT
= 'deg ').
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