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Converts a direction from ICRS to J2000 using the CASA measures tool and computes the angular separation.
See also J2000ToICRS
. As discussed in CAS-7885
, the optically-defined FK5 frame differs from ICRS by a maximum of 31.57 mas, while the CASA J2000 frame differs from ICRS by 23.15 mas. Note that J2000 is also used as a name to label the epoch that corresponds to 2000-Jan-01 at 12h UT. In ALMA Cycles 0-3, the antennas point in the FK5 frame, while the delays are pointed in the ICRS frame. In Cycle 4, the antennas will also point in the ICRS frame.
au.ICRSToJ2000(radec, date='', verbose=True)
- radec: sexagesimal string format
- date: optional -- CASA shows no date dependence in this calculation! Any of these formats is valid (The time portion is optional):
- 2011/10/15 05:00:00
- 2011-10-15 05:00:00
CASA <10>: au.ICRSToJ2000('18:37:24.5088 -33:19:08.760')
Separation: radian = 2.33282e-08, degrees = 0.000001, arcsec = 0.004812
Out: '18:37:24.50901, -033:19:08.755972'