[AstroPy] Need some advise about inputting a old coordinate

Paul Kuin npkuin at gmail.com
Thu Nov 24 18:55:22 EST 2016


I have a coordinate ra, dec in (1900) which I assume is
the B1900 equinox. If I put that in the SkyCoord call it does
seem to default to ICRS. Its not FK4 or FK5, so how do I enter
that coordinate?  Can someone help me, please?

What I did so far - things that work is when the frame is ICRS or FK4:

pos = coordinates.SkyCoord(FK4(ra=Angle("5h11.5m"), dec=Angle("-71d46m")),)
and
p2000=pos.transform_to("icrs")
with
pos
<SkyCoord (FK4: equinox=B1950.000, obstime=B1950.000): (ra, dec) in deg
    (77.875, -71.76666667)>
and
p2000
<SkyCoord (ICRS): (ra, dec) in deg
    (77.69083577, -71.70770648)>

That all works but it is not a B1950 frame, unfortunately, but B1900.

p1900 = coordinates.SkyCoord(ra=Angle("5h11.5m"),
dec=Angle("-71d46m"),equinox=astropy.time.Time(2415020.3135,format="jd"))
 p1900
<SkyCoord (ICRS): (ra, dec) in deg
 (77.875, -71.76666667)>

I hope I'm not too confusing, but it seems not possible. Any help is
being appreciated!

Cheers,
   Paul


-- 

* * * * * * * * http://www.mssl.ucl.ac.uk/~npmk/ * * * *
Dr. N.P.M. Kuin      (n.kuin at ucl.ac.uk)
phone +44-(0)1483 (prefix) -204111 (work)
mobile +44(0)7908715953  skype ID: npkuin
Mullard Space Science Laboratory  – University College London  –
Holmbury St Mary – Dorking – Surrey RH5 6NT–  U.K.



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