[fitsbits] FIT Keyword data dictionaries

[Doug Mink]

Mark Calabretta wrote:
> 
> On Mon 2000/11/06 08:48:08 -0000, Patrick Wallace wrote

> >The real bugbear is azimuth, where a left-handed convention (north thru
> >east) is firmly established.
> 
> Quite true.  WCS paper 2 says to encode it as a negative azimuth (and use
> elevation rather than zenith distance) though it also points out the
> possibility of flipping projection plane coordinates via the CD matrix and
> using positive azimuth.  However, it doesn't specify coordinate system
> codes for either (they would have to be distinguishable) nor for (HA,dec)
> since maps aren't drawn in these coordinates.

I actually had occasion to generate images of the sky at a specific historical
time, and it seemed appropriate to generate them in alt-az coordinates.  Here
is the relevant portion of the header I wrote for a south-centered image of
the sky as seen on a specific night in Rome:

DATE-OBS= '1611-04-15'
UT      = '00:00:00'
CTYPE1  = 'AZ---LIN'
CTYPE2  = 'ALT--LIN'
CRPIX1  =                 1080
CRPIX2  =                  270
CRVAL1  =                180.0
CRVAL2  =                 45.0
CDELT1  =            0.1666667
CDELT2  =            0.1666667


-Doug Mink