[fitsbits] Hour angle / Declination

[Steve Allen]

On Mon 2004-07-19T10:52:45 +0200, Jennifer Hatchell hath writ:

> Is there a standard CTYPE notation for hour angle and declination?

No.

If there were it would have to disambiguate numerous issues.

Would it be the values as reported by a telescope pointing system?
If so, would those be raw encoder values or re-reduced and registered ones?

Would it include the effects of refraction?

Would it include the effects of diurnal aberration?

How would it specify the implied coordinates of the observer?
Geocentric?  Astronomical?  Geodetic?

Would its values be calculated using the old Newcomb expressions
which became invalid in 1984?
The Aoki et al. expressions which became invalid in 2003?
The new CEO/TEO expressions which imply a whole new nomenclature?

On the other hand, there is nothing preventing the informal use of
local conventions for those keyword values.

--
Steve Allen          UCO/Lick Observatory       Santa Cruz, CA 95064
sla at ucolick.org      Voice: +1 831 459 3046     http://www.ucolick.org/~sla
PGP: 1024/E46978C5   F6 78 D1 10 62 94 8F 2E    49 89 0E FE 26 B4 14 93