[AstroPy] Telescope pointing with astropy, atmospheric refraction, and precession

[Stuart P Littlefair]

That's great Tony!

We're always interested in more comparisons to benchmark the astropy code
against.

There has been a lot of recent progress on this front; astropy 4.2 has an
"apparent" RA/Dec frame (TETE) included and we hope to include the HA/Dec
frame in 4.3. We have also been working on comparison to Skyfield and can
get very precise (fractions of milli-arcseconds between the two). These
changes should appear in 4.3 as well.

For these kind of precisions you need to use the JPL ephemerides with
astropy. I'd be very interested to see a comparison with CASA measures.
Would you be prepared to post the values you get from the CASA measures
tool?

On Tue, 1 Dec 2020 at 01:03, Tony Willis <tony.willis.research at gmail.com>
wrote:

> I've been following this thread with interest. About 2 years ago I went
> through the effort of computing and comparing apparent position
> calculations from astropy, skyfield, PyEphem and CASA Measures. I'm
> attaching the script I used to test the output using the radio source
> 3C147. Lines up to about 160 just have some conversion functions I put
> in so the script was more or less self-contained. The actual tests begin
> at about line 161. The outputs generally agree to within about 0.5 arcs
> or so. Personally I tend to use CASA Measures code for this sort of
> thing. That particular part of CASA was written by Wim Brouw, who used
> to be on the IAU SOFA board. But both astropy and skyfield give very
> close answers.
>
> Cheers
>
> Tony Willis
>
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>


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Stuart Littlefair

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email: S.Littlefair at sheffield.ac.uk
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