HFWG Recommendation R3:
On standard RA and DEC keywords giving the position of the observed object, the telescope pointing, and the spacecraft axes(Approved: 1993 Jun 30)
A) Reference Frame Keywords
Both of the following keywords are mandatory if one or more pairs of keywords specifying RA and dec (as defined in B) are given.
B) The RA and Dec Coordinates
In all cases listed below, the values of keywords are reals expressed in
decimal degrees. Obviously only those keyword pairs considered
necessary need be specified. However, the values of ALL such keyword
pairs MUST be given in the same reference frame as specified by the
values of the
i) The Positions of Astronomical Objects/Sources
The position of an astronomical source should be given using the keywords:
ii) The Pointing Direction of the Instrument.
The pointing direction of the instrument should be given using the keywords:
For instruments with less than 100% stable pointing accuracy, the above pair of keywords should be the mean values during the observation.
iii) The Orientation of the Spacecraft
The orientation of the spacecraft (or telescope platform) should be given by the specification of any/all of the following keyword pairs:
giving the orientation of the spacecraft X-, Y- and Z-axes respectively. For instruments with less than 100% stable pointing accuracy, the above pairs of keywords should be the mean values during the observation.