[AstroPy] AstroPy Digest, Vol 171, Issue 1

[Tony Willis]

Hi Stuart

Sure - tell me exactly what you would like done.

Tony

On 2020-12-01 9:00 a.m., astropy-request at python.org wrote:
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> Today's Topics:
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>     1. Re: Telescope pointing with astropy, atmospheric refraction,
>        and precession (Stuart P Littlefair)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Tue, 1 Dec 2020 09:55:52 +0000
> From: Stuart P Littlefair <s.littlefair at sheffield.ac.uk>
> To: Astronomical Python mailing list <astropy at python.org>
> Subject: Re: [AstroPy] Telescope pointing with astropy, atmospheric
> 	refraction, and precession
> Message-ID:
> 	<CAOrDc-9JOPrd9fAhfEr5Uwd5J_v07O-iu5b1EdNEER0uGoGPgg at mail.gmail.com>
> Content-Type: text/plain; charset="utf-8"
>
> 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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