> Frame title : "ICRS coordinates; gnomonic projection"
> Domain : SKY
> System : ICRS
> Ref. position (RA,Dec): 1:29:04.1, -55:37:12
> Projection : gnomonic
> Epoch of observation: J2000 (1-JAN-2000 12:0:0) TDB
"Epoch of observation" is almost certain wrong, and should be based
on the date and time of the exposure.
"J2000" presumably means "J2000.0" which was the epoch of the FK5
precessing equator and ecliptic that was the forerunner to ICRS.
The latter is defined by distant sources and is completely unrelated
to Earth orientation; consequently it has no epoch or equinox. As
it turned out, ICRS is askew from FK5 by just under 25 mas; the
relative orientation is called "frame bias".
Patrick Wallace
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RAL Space +44-1235-531198
STFC Rutherford Appleton Laboratory
Harwell Oxford
Didcot, Oxfordshire, OX11 0QX, UK [log in to unmask]
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