From bsipocz at gmail.com  Sun Nov  8 02:21:27 2020
From: bsipocz at gmail.com (Brigitta Sipocz)
Date: Sat, 7 Nov 2020 23:21:27 -0800
Subject: [AstroPy] astropy v4.2rc1 release candidate testing
Message-ID: <CAEjJ3fhDBXi+H6etMoFNx8=u6pCM45QHnchaAu72x8dnRPGD6g@mail.gmail.com>

Dear All,

The first astropy v4.2 release candidate is now available and ready for
testing.

https://pypi.python.org/pypi/astropy/4.2rc1

We would appreciate if you could try out this RC and report back any
success or failure via the following wiki page. If you maintain any
downstream packages please check, and preferably whether they are
compatible or there are any blocking issues:

https://github.com/astropy/astropy/wiki/v4.2-RC-testing

Please also, open issues for each different type of failure (please check
the issue tracker first to make sure no one has reported it earlier). In
addition to running the astropy test suite itself, we especially encourage
you to also test it with as many packages of yours as possible. There is a
section to list packages at the bottom of the wiki page.

You should be able to install the RC by doing:

pip install astropy --pre

or

pip install astropy==4.2rc1

If you use conda, be sure to either remove the existing conda astropy
package or make a new environment.

Happy testing,
 Brigitta
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From omega.centauri at gmail.com  Wed Nov 18 13:26:14 2020
From: omega.centauri at gmail.com (Nicola Montecchiari)
Date: Wed, 18 Nov 2020 19:26:14 +0100
Subject: [AstroPy] IERS issue again
Message-ID: <CADMj6LBDyYmUfmADk3GYUP17RZT_PgLhWw1USdP2+ojnVeJNQg@mail.gmail.com>

Hello everybody,

after some months I am getting again an error while trying to connect to
the IERS.

Python 2.7.18 (v2.7.18:8d21aa21f2, Apr 20 2020, 13:19:08) [MSC v.1500 32
bit (Intel)] on win32
astropy==2.0.16
numpy==1.16.6

>>> from astropy.time import Time
>>> t = Time('2016:001')
>>> t.ut1
WARNING: failed to download
https://datacenter.iers.org/data/9/finals2000A.all and
ftp://cddis.gsfc.nasa.gov/pub/products/iers/finals2000A.all, using local
IERS-B: <urlopen error [SSL: CERTIFICATE_VERIFY_FAILED] certificate verify
failed (_ssl.c:727)>;<urlopen error ftp error: timed out>
[astropy.utils.iers.iers]
<Time object: scale='ut1' format='yday' value=2016:001:00:00:00.082>

Is this a known issue?
Thanks a lot for your help
Nicola

<https://www.avast.com/sig-email?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail>
Mail
priva di virus. www.avast.com
<https://www.avast.com/sig-email?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail>
<#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2>
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From erik.m.bray at gmail.com  Sun Nov 22 13:03:36 2020
From: erik.m.bray at gmail.com (E. Madison Bray)
Date: Sun, 22 Nov 2020 19:03:36 +0100
Subject: [AstroPy] IERS issue again
In-Reply-To: <CADMj6LBDyYmUfmADk3GYUP17RZT_PgLhWw1USdP2+ojnVeJNQg@mail.gmail.com>
References: <CADMj6LBDyYmUfmADk3GYUP17RZT_PgLhWw1USdP2+ojnVeJNQg@mail.gmail.com>
Message-ID: <CAOTD34Ye_U21aHgj=wpZd_MRmVhR6_Cn__599AWOhH5Vg3tbMQ@mail.gmail.com>

Hi Nicolas,

Apologies for the late response. A few things:

1) I'm sorry you hate this particularly annoying problem.  It's especially
prevalent on Windows, where Python itself ships some SSL root certificates
to use to verify SSL resources on the internet.  Unfortunately if your
Python installation is too old, the certificates it ships with might be
expired.

2) It looks like you're using a very old version of Astropy, on Python 2.7,
which is deprecated.  As soon as possible you should upgrade to Python 3;
Python 3.7 is probably the most stable for most software you use, if not
Python 3.8.

3) That said, you might be stuck on Python 2.7 for reasons I cannot know.
And even if you were on a newer version of Python it might still be a
problem.  This is a known issue in Astropy which has a fix at [1] which
will be included in Astropy v4.3.0

4) There is a potential workaround, though mind you I have not tested it
since I don't have Python 2.7 on Windows anymore.  The workaround is to use
the certifi [2] package, which provides up-to-date SSL root certificates in
a manner which is easy to use by Python [3].  Its source releases should
still work on Python 2.7.  The next step is you need to "monkey patch" the
`ssl` module of Python to ensure that it always uses the certificates from
certifi.  Here's a way you can do that; you would run this in your script
before trying to do anything with astropy.time:

First you need to install certifi:

```
> python2.7 -m pip install certifi
```

Then in your Python code:

```
import certifi
import ssl
orig_create_default_context = ssl.create_default_context

def create_default_context(**kwargs):
    kwargs['cafile'] = certifi.where()
    return orig_create_default_context(**kwargs)

ssl.create_default_context = create_default_context
```

I believe this should work, but again I stress that it is untested.  Give
it a try and see if it resolves the issue for you, and please report back
here whether it works or not.

Nevertheless I would encourage you to upgrade to Python 3 as soon as
possible.

Best,
Madison

[1] https://github.com/astropy/astropy/pull/10434
[2] https://pypi.org/project/certifi/

On Wed, Nov 18, 2020 at 7:26 PM Nicola Montecchiari <
omega.centauri at gmail.com> wrote:

> Hello everybody,
>
> after some months I am getting again an error while trying to connect to
> the IERS.
>
> Python 2.7.18 (v2.7.18:8d21aa21f2, Apr 20 2020, 13:19:08) [MSC v.1500 32
> bit (Intel)] on win32
> astropy==2.0.16
> numpy==1.16.6
>
> >>> from astropy.time import Time
> >>> t = Time('2016:001')
> >>> t.ut1
> WARNING: failed to download
> https://datacenter.iers.org/data/9/finals2000A.all and
> ftp://cddis.gsfc.nasa.gov/pub/products/iers/finals2000A.all, using local
> IERS-B: <urlopen error [SSL: CERTIFICATE_VERIFY_FAILED] certificate verify
> failed (_ssl.c:727)>;<urlopen error ftp error: timed out>
> [astropy.utils.iers.iers]
> <Time object: scale='ut1' format='yday' value=2016:001:00:00:00.082>
>
> Is this a known issue?
> Thanks a lot for your help
> Nicola
>
>
> <https://www.avast.com/sig-email?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail> Mail
> priva di virus. www.avast.com
> <https://www.avast.com/sig-email?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail>
> <#m_-2678403154958117125_DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2>
> _______________________________________________
> AstroPy mailing list
> AstroPy at python.org
> https://mail.python.org/mailman/listinfo/astropy
>
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From erik.m.bray at gmail.com  Sun Nov 22 13:04:18 2020
From: erik.m.bray at gmail.com (E. Madison Bray)
Date: Sun, 22 Nov 2020 19:04:18 +0100
Subject: [AstroPy] IERS issue again
In-Reply-To: <CAOTD34Ye_U21aHgj=wpZd_MRmVhR6_Cn__599AWOhH5Vg3tbMQ@mail.gmail.com>
References: <CADMj6LBDyYmUfmADk3GYUP17RZT_PgLhWw1USdP2+ojnVeJNQg@mail.gmail.com>
 <CAOTD34Ye_U21aHgj=wpZd_MRmVhR6_Cn__599AWOhH5Vg3tbMQ@mail.gmail.com>
Message-ID: <CAOTD34a1UL5Rd-qHUXSFcJkvcQ4+w2v8gVyzLppa1eXgEDOxDg@mail.gmail.com>

Hi *Nicola

(Sorry, I'm in France, so same name different spelling)

On Sun, Nov 22, 2020 at 7:03 PM E. Madison Bray <erik.m.bray at gmail.com>
wrote:

> Hi Nicolas,
>
> Apologies for the late response. A few things:
>
> 1) I'm sorry you hate this particularly annoying problem.  It's especially
> prevalent on Windows, where Python itself ships some SSL root certificates
> to use to verify SSL resources on the internet.  Unfortunately if your
> Python installation is too old, the certificates it ships with might be
> expired.
>
> 2) It looks like you're using a very old version of Astropy, on Python
> 2.7, which is deprecated.  As soon as possible you should upgrade to Python
> 3; Python 3.7 is probably the most stable for most software you use, if not
> Python 3.8.
>
> 3) That said, you might be stuck on Python 2.7 for reasons I cannot know.
> And even if you were on a newer version of Python it might still be a
> problem.  This is a known issue in Astropy which has a fix at [1] which
> will be included in Astropy v4.3.0
>
> 4) There is a potential workaround, though mind you I have not tested it
> since I don't have Python 2.7 on Windows anymore.  The workaround is to use
> the certifi [2] package, which provides up-to-date SSL root certificates in
> a manner which is easy to use by Python [3].  Its source releases should
> still work on Python 2.7.  The next step is you need to "monkey patch" the
> `ssl` module of Python to ensure that it always uses the certificates from
> certifi.  Here's a way you can do that; you would run this in your script
> before trying to do anything with astropy.time:
>
> First you need to install certifi:
>
> ```
> > python2.7 -m pip install certifi
> ```
>
> Then in your Python code:
>
> ```
> import certifi
> import ssl
> orig_create_default_context = ssl.create_default_context
>
> def create_default_context(**kwargs):
>     kwargs['cafile'] = certifi.where()
>     return orig_create_default_context(**kwargs)
>
> ssl.create_default_context = create_default_context
> ```
>
> I believe this should work, but again I stress that it is untested.  Give
> it a try and see if it resolves the issue for you, and please report back
> here whether it works or not.
>
> Nevertheless I would encourage you to upgrade to Python 3 as soon as
> possible.
>
> Best,
> Madison
>
> [1] https://github.com/astropy/astropy/pull/10434
> [2] https://pypi.org/project/certifi/
>
> On Wed, Nov 18, 2020 at 7:26 PM Nicola Montecchiari <
> omega.centauri at gmail.com> wrote:
>
>> Hello everybody,
>>
>> after some months I am getting again an error while trying to connect to
>> the IERS.
>>
>> Python 2.7.18 (v2.7.18:8d21aa21f2, Apr 20 2020, 13:19:08) [MSC v.1500 32
>> bit (Intel)] on win32
>> astropy==2.0.16
>> numpy==1.16.6
>>
>> >>> from astropy.time import Time
>> >>> t = Time('2016:001')
>> >>> t.ut1
>> WARNING: failed to download
>> https://datacenter.iers.org/data/9/finals2000A.all and
>> ftp://cddis.gsfc.nasa.gov/pub/products/iers/finals2000A.all, using local
>> IERS-B: <urlopen error [SSL: CERTIFICATE_VERIFY_FAILED] certificate verify
>> failed (_ssl.c:727)>;<urlopen error ftp error: timed out>
>> [astropy.utils.iers.iers]
>> <Time object: scale='ut1' format='yday' value=2016:001:00:00:00.082>
>>
>> Is this a known issue?
>> Thanks a lot for your help
>> Nicola
>>
>>
>> <https://www.avast.com/sig-email?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail> Mail
>> priva di virus. www.avast.com
>> <https://www.avast.com/sig-email?utm_medium=email&utm_source=link&utm_campaign=sig-email&utm_content=webmail>
>> <#m_841604273680308995_m_-2678403154958117125_DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2>
>> _______________________________________________
>> AstroPy mailing list
>> AstroPy at python.org
>> https://mail.python.org/mailman/listinfo/astropy
>>
>
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From russell.valentine at gmail.com  Fri Nov 27 16:20:13 2020
From: russell.valentine at gmail.com (Russell Valentine)
Date: Fri, 27 Nov 2020 15:20:13 -0600
Subject: [AstroPy] Telescope pointing with astropy,
 atmospheric refraction and precession
Message-ID: <cd2ddd21-85d3-1007-0fd9-e0e12453f7e7@gmail.com>

Hello,

I've been trying to figure out the best way to get correct coordinates 
for telescope pointing of a equatorial mount in astropy. How to, given a 
set of coordinates in ICRS, convert it to account for precession and 
atmosphereic refraction to correctly move the telescope. It is my 
understand that you can transform from ICRS to TETE to compensate for 
precession, but then how to also account for atmospheric refraction? I 
believe the AltAz coordinate is needed for that.

Things I was thinking and tried:

1) ICRS->AltAz (w/pressure)->TETE
I do not know if this is correct because you get just very close to just 
ICRS. I thought maybe it is right and the refraction just happens to be 
the counter the precession, but I tried it on both east and west 
horizons with the same result.

2) ICRS->TETE->AltAz(w/pressure)

But as expected AltAz is the same as ICRS->AltAz

I feel like I am missing some key piece. Has anyone done this with astropy?




from astropy.coordinates import EarthLocation, TETE, ICRS, AltAz, SkyCoord
import astropy.units as u
from astropy.time import Time as AstroTime
from astropy.units import si as usi
t = AstroTime('2020-11-27 19:12:16.894431')
earth_location = EarthLocation(lat=38.9369*u.deg, lon= -95.242*u.deg, 
height=266.0*u.m)
# East horizon object
icrs = ICRS(ra=346.23611667*u.deg, dec=12.32287778*u.deg)
pressure = 98170.13549857 * u.Pa
altaz = icrs.transform_to(AltAz(obstime=t, location=earth_location, 
pressure=pressure))
tete = icrs.transform_to(TETE(obstime=t, location=earth_location))
tete_from_altaz = altaz.transform_to(TETE())

# West horizon object
icrs2 = ICRS(ra=172.53106667*u.deg, dec=9.27663056*u.deg)
altaz2 = icrs2.transform_to(AltAz(obstime=t, location=earth_location, 
pressure=pressure))
tete2 = icrs2.transform_to(TETE(obstime=t, location=earth_location))
tete2_from_altaz2 = altaz2.transform_to(TETE())


altaz_from_tete = tete_from_altaz.transform_to(AltAz(obstime=t, 
location=earth_location, pressure=pressure))

From ejensen1 at swarthmore.edu  Fri Nov 27 21:24:14 2020
From: ejensen1 at swarthmore.edu (Eric Jensen)
Date: Fri, 27 Nov 2020 21:24:14 -0500
Subject: [AstroPy] Telescope pointing with astropy,
 atmospheric refraction and precession
In-Reply-To: <cd2ddd21-85d3-1007-0fd9-e0e12453f7e7@gmail.com>
References: <cd2ddd21-85d3-1007-0fd9-e0e12453f7e7@gmail.com>
Message-ID: <45E6EAB3-E1EA-4C3E-8E00-9AAF6E60DDF6@swarthmore.edu>

Hi Russell, 

I think the thing you?re missing may be the ?equinox? argument to the ?transform_to? call.  I believe that ?obstime? sets the time of your observation for calculating alt/az (and may also be used as the reference date for applying proper motion corrections if you do that), but I don?t think it sets the date for the equinox used for your coordinate system.  Try adding ?equinox=t? to your transformations between ICRS and TETE and see if that helps.    (I can?t test here because conda channels haven?t caught up with the 4.2 release yet, so I don?t have TETE in my installation.) 

Best,

Eric
 

> On Nov 27, 2020, at 4:20 PM, Russell Valentine <russell.valentine at gmail.com> wrote:
> 
> Hello,
> 
> I've been trying to figure out the best way to get correct coordinates for telescope pointing of a equatorial mount in astropy. How to, given a set of coordinates in ICRS, convert it to account for precession and atmosphereic refraction to correctly move the telescope. It is my understand that you can transform from ICRS to TETE to compensate for precession, but then how to also account for atmospheric refraction? I believe the AltAz coordinate is needed for that.
> 
> Things I was thinking and tried:
> 
> 1) ICRS->AltAz (w/pressure)->TETE
> I do not know if this is correct because you get just very close to just ICRS. I thought maybe it is right and the refraction just happens to be the counter the precession, but I tried it on both east and west horizons with the same result.
> 
> 2) ICRS->TETE->AltAz(w/pressure)
> 
> But as expected AltAz is the same as ICRS->AltAz
> 
> I feel like I am missing some key piece. Has anyone done this with astropy?
> 
> 
> 
> 
> from astropy.coordinates import EarthLocation, TETE, ICRS, AltAz, SkyCoord
> import astropy.units as u
> from astropy.time import Time as AstroTime
> from astropy.units import si as usi
> t = AstroTime('2020-11-27 19:12:16.894431')
> earth_location = EarthLocation(lat=38.9369*u.deg, lon= -95.242*u.deg, height=266.0*u.m)
> # East horizon object
> icrs = ICRS(ra=346.23611667*u.deg, dec=12.32287778*u.deg)
> pressure = 98170.13549857 * u.Pa
> altaz = icrs.transform_to(AltAz(obstime=t, location=earth_location, pressure=pressure))
> tete = icrs.transform_to(TETE(obstime=t, location=earth_location))
> tete_from_altaz = altaz.transform_to(TETE())
> 
> # West horizon object
> icrs2 = ICRS(ra=172.53106667*u.deg, dec=9.27663056*u.deg)
> altaz2 = icrs2.transform_to(AltAz(obstime=t, location=earth_location, pressure=pressure))
> tete2 = icrs2.transform_to(TETE(obstime=t, location=earth_location))
> tete2_from_altaz2 = altaz2.transform_to(TETE())
> 
> 
> altaz_from_tete = tete_from_altaz.transform_to(AltAz(obstime=t, location=earth_location, pressure=pressure))
> _______________________________________________
> AstroPy mailing list
> AstroPy at python.org
> https://mail.python.org/mailman/listinfo/astropy


From russell.valentine at gmail.com  Sat Nov 28 01:46:03 2020
From: russell.valentine at gmail.com (Russell Valentine)
Date: Sat, 28 Nov 2020 00:46:03 -0600
Subject: [AstroPy] Telescope pointing with astropy,
 atmospheric refraction and precession
In-Reply-To: <45E6EAB3-E1EA-4C3E-8E00-9AAF6E60DDF6@swarthmore.edu>
References: <cd2ddd21-85d3-1007-0fd9-e0e12453f7e7@gmail.com>
 <45E6EAB3-E1EA-4C3E-8E00-9AAF6E60DDF6@swarthmore.edu>
Message-ID: <53fc5305-365d-6521-1060-1fcd7865e6ab@gmail.com>

Thank you for your reply Eric. I do not think TETE can take a equinox 
parameter. I know FK5 has one. I do see what I think is precession 
corrections when I go from ICRS to TETE, however I do not think TETE 
does atmospheric refraction as well.

https://docs.astropy.org/en/stable/api/astropy.coordinates.builtin_frames.TETE.html#astropy.coordinates.builtin_frames.TETE


 >>> tete = icrs.transform_to(TETE(obstime=t, location=earth_location, 
equinox=t))
Traceback (most recent call last):
   File "<stdin>", line 1, in <module>
   File 
"/home/russ/.local/share/virtualenvs/server-zkliv1pZ/lib/python3.7/site-packages/astropy/coordinates/baseframe.py", 
line 609, in __init__
     list(kwargs)))
TypeError: Coordinate frame got unexpected keywords: ['equinox']


On 11/27/20 8:24 PM, Eric Jensen wrote:
> Hi Russell,
> 
> I think the thing you?re missing may be the ?equinox? argument to the ?transform_to? call.  I believe that ?obstime? sets the time of your observation for calculating alt/az (and may also be used as the reference date for applying proper motion corrections if you do that), but I don?t think it sets the date for the equinox used for your coordinate system.  Try adding ?equinox=t? to your transformations between ICRS and TETE and see if that helps.    (I can?t test here because conda channels haven?t caught up with the 4.2 release yet, so I don?t have TETE in my installation.)
> 
> Best,
> 
> Eric
>   
> 
>> On Nov 27, 2020, at 4:20 PM, Russell Valentine <russell.valentine at gmail.com> wrote:
>>
>> Hello,
>>
>> I've been trying to figure out the best way to get correct coordinates for telescope pointing of a equatorial mount in astropy. How to, given a set of coordinates in ICRS, convert it to account for precession and atmosphereic refraction to correctly move the telescope. It is my understand that you can transform from ICRS to TETE to compensate for precession, but then how to also account for atmospheric refraction? I believe the AltAz coordinate is needed for that.
>>
>> Things I was thinking and tried:
>>
>> 1) ICRS->AltAz (w/pressure)->TETE
>> I do not know if this is correct because you get just very close to just ICRS. I thought maybe it is right and the refraction just happens to be the counter the precession, but I tried it on both east and west horizons with the same result.
>>
>> 2) ICRS->TETE->AltAz(w/pressure)
>>
>> But as expected AltAz is the same as ICRS->AltAz
>>
>> I feel like I am missing some key piece. Has anyone done this with astropy?
>>
>>
>>
>>
>> from astropy.coordinates import EarthLocation, TETE, ICRS, AltAz, SkyCoord
>> import astropy.units as u
>> from astropy.time import Time as AstroTime
>> from astropy.units import si as usi
>> t = AstroTime('2020-11-27 19:12:16.894431')
>> earth_location = EarthLocation(lat=38.9369*u.deg, lon= -95.242*u.deg, height=266.0*u.m)
>> # East horizon object
>> icrs = ICRS(ra=346.23611667*u.deg, dec=12.32287778*u.deg)
>> pressure = 98170.13549857 * u.Pa
>> altaz = icrs.transform_to(AltAz(obstime=t, location=earth_location, pressure=pressure))
>> tete = icrs.transform_to(TETE(obstime=t, location=earth_location))
>> tete_from_altaz = altaz.transform_to(TETE())
>>
>> # West horizon object
>> icrs2 = ICRS(ra=172.53106667*u.deg, dec=9.27663056*u.deg)
>> altaz2 = icrs2.transform_to(AltAz(obstime=t, location=earth_location, pressure=pressure))
>> tete2 = icrs2.transform_to(TETE(obstime=t, location=earth_location))
>> tete2_from_altaz2 = altaz2.transform_to(TETE())
>>
>>
>> altaz_from_tete = tete_from_altaz.transform_to(AltAz(obstime=t, location=earth_location, pressure=pressure))
>> _______________________________________________
>> AstroPy mailing list
>> AstroPy at python.org
>> https://mail.python.org/mailman/listinfo/astropy
> 
> _______________________________________________
> AstroPy mailing list
> AstroPy at python.org
> https://mail.python.org/mailman/listinfo/astropy
> 

From s.littlefair at sheffield.ac.uk  Sat Nov 28 03:53:09 2020
From: s.littlefair at sheffield.ac.uk (Stuart P Littlefair)
Date: Sat, 28 Nov 2020 08:53:09 +0000
Subject: [AstroPy] Telescope pointing with astropy,
 atmospheric refraction and precession
In-Reply-To: <53fc5305-365d-6521-1060-1fcd7865e6ab@gmail.com>
References: <53fc5305-365d-6521-1060-1fcd7865e6ab@gmail.com>
Message-ID: <952F1896-68C1-4D35-8780-4181F3F80260@sheffield.ac.uk>

Hi Russel

You are correct that TETE does not include atmospheric refraction. What you want is an HA-Dec frame. 

It does not exist within astropy yet, but is on the roadmap for the near future. 

If you want something to work in the meantime, you could look at the code in coordinates/builtin_frames/icrs_observed.py in the current master branch on GitHub. 

This file contains the transforms from ICRS to AltAz and you will see that it actually calculates the HA as part of the function!

You could simply copy this function and return HA and Dec instead of Alt and Az. 

Stuart Littlefair
Dept. of Physics & Astronomy
Univ. of Sheffield, Sheffield, S3 7RH

email: s.littlefair at shef.ac.uk
Phone: +44 114 2224525
Sent from my iPhone

> On 28 Nov 2020, at 06:46, Russell Valentine <russell.valentine at gmail.com> wrote:
> 
> ?Thank you for your reply Eric. I do not think TETE can take a equinox parameter. I know FK5 has one. I do see what I think is precession corrections when I go from ICRS to TETE, however I do not think TETE does atmospheric refraction as well.
> 
> https://docs.astropy.org/en/stable/api/astropy.coordinates.builtin_frames.TETE.html#astropy.coordinates.builtin_frames.TETE
> 
> 
> >>> tete = icrs.transform_to(TETE(obstime=t, location=earth_location, equinox=t))
> Traceback (most recent call last):
>  File "<stdin>", line 1, in <module>
>  File "/home/russ/.local/share/virtualenvs/server-zkliv1pZ/lib/python3.7/site-packages/astropy/coordinates/baseframe.py", line 609, in __init__
>    list(kwargs)))
> TypeError: Coordinate frame got unexpected keywords: ['equinox']
> 
> 
>> On 11/27/20 8:24 PM, Eric Jensen wrote:
>> Hi Russell,
>> I think the thing you?re missing may be the ?equinox? argument to the ?transform_to? call.  I believe that ?obstime? sets the time of your observation for calculating alt/az (and may also be used as the reference date for applying proper motion corrections if you do that), but I don?t think it sets the date for the equinox used for your coordinate system.  Try adding ?equinox=t? to your transformations between ICRS and TETE and see if that helps.    (I can?t test here because conda channels haven?t caught up with the 4.2 release yet, so I don?t have TETE in my installation.)
>> Best,
>> Eric
>>  
>>>> On Nov 27, 2020, at 4:20 PM, Russell Valentine <russell.valentine at gmail.com> wrote:
>>> 
>>> Hello,
>>> 
>>> I've been trying to figure out the best way to get correct coordinates for telescope pointing of a equatorial mount in astropy. How to, given a set of coordinates in ICRS, convert it to account for precession and atmosphereic refraction to correctly move the telescope. It is my understand that you can transform from ICRS to TETE to compensate for precession, but then how to also account for atmospheric refraction? I believe the AltAz coordinate is needed for that.
>>> 
>>> Things I was thinking and tried:
>>> 
>>> 1) ICRS->AltAz (w/pressure)->TETE
>>> I do not know if this is correct because you get just very close to just ICRS. I thought maybe it is right and the refraction just happens to be the counter the precession, but I tried it on both east and west horizons with the same result.
>>> 
>>> 2) ICRS->TETE->AltAz(w/pressure)
>>> 
>>> But as expected AltAz is the same as ICRS->AltAz
>>> 
>>> I feel like I am missing some key piece. Has anyone done this with astropy?
>>> 
>>> 
>>> 
>>> 
>>> from astropy.coordinates import EarthLocation, TETE, ICRS, AltAz, SkyCoord
>>> import astropy.units as u
>>> from astropy.time import Time as AstroTime
>>> from astropy.units import si as usi
>>> t = AstroTime('2020-11-27 19:12:16.894431')
>>> earth_location = EarthLocation(lat=38.9369*u.deg, lon= -95.242*u.deg, height=266.0*u.m)
>>> # East horizon object
>>> icrs = ICRS(ra=346.23611667*u.deg, dec=12.32287778*u.deg)
>>> pressure = 98170.13549857 * u.Pa
>>> altaz = icrs.transform_to(AltAz(obstime=t, location=earth_location, pressure=pressure))
>>> tete = icrs.transform_to(TETE(obstime=t, location=earth_location))
>>> tete_from_altaz = altaz.transform_to(TETE())
>>> 
>>> # West horizon object
>>> icrs2 = ICRS(ra=172.53106667*u.deg, dec=9.27663056*u.deg)
>>> altaz2 = icrs2.transform_to(AltAz(obstime=t, location=earth_location, pressure=pressure))
>>> tete2 = icrs2.transform_to(TETE(obstime=t, location=earth_location))
>>> tete2_from_altaz2 = altaz2.transform_to(TETE())
>>> 
>>> 
>>> altaz_from_tete = tete_from_altaz.transform_to(AltAz(obstime=t, location=earth_location, pressure=pressure))
>>> _______________________________________________
>>> AstroPy mailing list
>>> AstroPy at python.org
>>> https://mail.python.org/mailman/listinfo/astropy
>> _______________________________________________
>> AstroPy mailing list
>> AstroPy at python.org
>> https://mail.python.org/mailman/listinfo/astropy
> _______________________________________________
> AstroPy mailing list
> AstroPy at python.org
> https://mail.python.org/mailman/listinfo/astropy

From russell.valentine at gmail.com  Sat Nov 28 13:29:36 2020
From: russell.valentine at gmail.com (Russell Valentine)
Date: Sat, 28 Nov 2020 12:29:36 -0600
Subject: [AstroPy] Telescope pointing with astropy,
 atmospheric refraction and precession
In-Reply-To: <952F1896-68C1-4D35-8780-4181F3F80260@sheffield.ac.uk>
References: <53fc5305-365d-6521-1060-1fcd7865e6ab@gmail.com>
 <952F1896-68C1-4D35-8780-4181F3F80260@sheffield.ac.uk>
Message-ID: <64ea1a7f-3ea8-74ae-981d-d6daf6eba6bc@gmail.com>

Yes, correct I do want HA-Dec frame.

I had been trying to do that on my own, but it was pretty convoluted. My 
current procedure was (psudocode):

side_real_time = AltAz(90,0, location, time).to(ICRS).ra
altaz = my_orig_coord.to(AltAz(location, pressure, time))
# Make new altaz without pressure and go back to icrs for
# refraction adjusted ra/dec
adjusted_icrs = AltAz(altaz.alot, altaz.az, location, time).to(ICRS)
adjusted_icrs = ICRS(side_real_time - adjusted_icrs.ra, adjusted_icrs.dec)

And then use adjusted_icrs.ra and adjusted_icrs.dec as telescope HA-DEC.

It was not clear to me if the altaz frame took into account precession. 
Maybe that happens when converting to topocentric CIRS.

Thank you for the reply and suggestion to look at icrs_observed.py I 
will do that, and try to learn more about these different coordinate 
systems.


Russell Valentine

On 11/28/20 2:53 AM, Stuart P Littlefair wrote:
> Hi Russel
> 
> You are correct that TETE does not include atmospheric refraction. What you want is an HA-Dec frame.
> 
> It does not exist within astropy yet, but is on the roadmap for the near future.
> 
> If you want something to work in the meantime, you could look at the code in coordinates/builtin_frames/icrs_observed.py in the current master branch on GitHub.
> 
> This file contains the transforms from ICRS to AltAz and you will see that it actually calculates the HA as part of the function!
> 
> You could simply copy this function and return HA and Dec instead of Alt and Az.
> 
> Stuart Littlefair
> Dept. of Physics & Astronomy
> Univ. of Sheffield, Sheffield, S3 7RH
> 
> email: s.littlefair at shef.ac.uk
> Phone: +44 114 2224525
> Sent from my iPhone
> 
>> On 28 Nov 2020, at 06:46, Russell Valentine <russell.valentine at gmail.com> wrote:
>>
>> ?Thank you for your reply Eric. I do not think TETE can take a equinox parameter. I know FK5 has one. I do see what I think is precession corrections when I go from ICRS to TETE, however I do not think TETE does atmospheric refraction as well.
>>
>> https://docs.astropy.org/en/stable/api/astropy.coordinates.builtin_frames.TETE.html#astropy.coordinates.builtin_frames.TETE
>>
>>
>>>>> tete = icrs.transform_to(TETE(obstime=t, location=earth_location, equinox=t))
>> Traceback (most recent call last):
>>   File "<stdin>", line 1, in <module>
>>   File "/home/russ/.local/share/virtualenvs/server-zkliv1pZ/lib/python3.7/site-packages/astropy/coordinates/baseframe.py", line 609, in __init__
>>     list(kwargs)))
>> TypeError: Coordinate frame got unexpected keywords: ['equinox']
>>
>>
>>> On 11/27/20 8:24 PM, Eric Jensen wrote:
>>> Hi Russell,
>>> I think the thing you?re missing may be the ?equinox? argument to the ?transform_to? call.  I believe that ?obstime? sets the time of your observation for calculating alt/az (and may also be used as the reference date for applying proper motion corrections if you do that), but I don?t think it sets the date for the equinox used for your coordinate system.  Try adding ?equinox=t? to your transformations between ICRS and TETE and see if that helps.    (I can?t test here because conda channels haven?t caught up with the 4.2 release yet, so I don?t have TETE in my installation.)
>>> Best,
>>> Eric
>>>   
>>>>> On Nov 27, 2020, at 4:20 PM, Russell Valentine <russell.valentine at gmail.com> wrote:
>>>>
>>>> Hello,
>>>>
>>>> I've been trying to figure out the best way to get correct coordinates for telescope pointing of a equatorial mount in astropy. How to, given a set of coordinates in ICRS, convert it to account for precession and atmosphereic refraction to correctly move the telescope. It is my understand that you can transform from ICRS to TETE to compensate for precession, but then how to also account for atmospheric refraction? I believe the AltAz coordinate is needed for that.
>>>>
>>>> Things I was thinking and tried:
>>>>
>>>> 1) ICRS->AltAz (w/pressure)->TETE
>>>> I do not know if this is correct because you get just very close to just ICRS. I thought maybe it is right and the refraction just happens to be the counter the precession, but I tried it on both east and west horizons with the same result.
>>>>
>>>> 2) ICRS->TETE->AltAz(w/pressure)
>>>>
>>>> But as expected AltAz is the same as ICRS->AltAz
>>>>
>>>> I feel like I am missing some key piece. Has anyone done this with astropy?
>>>>
>>>>
>>>>
>>>>
>>>> from astropy.coordinates import EarthLocation, TETE, ICRS, AltAz, SkyCoord
>>>> import astropy.units as u
>>>> from astropy.time import Time as AstroTime
>>>> from astropy.units import si as usi
>>>> t = AstroTime('2020-11-27 19:12:16.894431')
>>>> earth_location = EarthLocation(lat=38.9369*u.deg, lon= -95.242*u.deg, height=266.0*u.m)
>>>> # East horizon object
>>>> icrs = ICRS(ra=346.23611667*u.deg, dec=12.32287778*u.deg)
>>>> pressure = 98170.13549857 * u.Pa
>>>> altaz = icrs.transform_to(AltAz(obstime=t, location=earth_location, pressure=pressure))
>>>> tete = icrs.transform_to(TETE(obstime=t, location=earth_location))
>>>> tete_from_altaz = altaz.transform_to(TETE())
>>>>
>>>> # West horizon object
>>>> icrs2 = ICRS(ra=172.53106667*u.deg, dec=9.27663056*u.deg)
>>>> altaz2 = icrs2.transform_to(AltAz(obstime=t, location=earth_location, pressure=pressure))
>>>> tete2 = icrs2.transform_to(TETE(obstime=t, location=earth_location))
>>>> tete2_from_altaz2 = altaz2.transform_to(TETE())
>>>>
>>>>
>>>> altaz_from_tete = tete_from_altaz.transform_to(AltAz(obstime=t, location=earth_location, pressure=pressure))
>>>> _______________________________________________
>>>> AstroPy mailing list
>>>> AstroPy at python.org
>>>> https://mail.python.org/mailman/listinfo/astropy
>>> _______________________________________________
>>> AstroPy mailing list
>>> AstroPy at python.org
>>> https://mail.python.org/mailman/listinfo/astropy
>> _______________________________________________
>> AstroPy mailing list
>> AstroPy at python.org
>> https://mail.python.org/mailman/listinfo/astropy
> _______________________________________________
> AstroPy mailing list
> AstroPy at python.org
> https://mail.python.org/mailman/listinfo/astropy
> 

From russell.valentine at gmail.com  Sun Nov 29 16:37:39 2020
From: russell.valentine at gmail.com (Russell Valentine)
Date: Sun, 29 Nov 2020 15:37:39 -0600
Subject: [AstroPy] Telescope pointing with astropy,
 atmospheric refraction and precession
In-Reply-To: <64ea1a7f-3ea8-74ae-981d-d6daf6eba6bc@gmail.com>
References: <53fc5305-365d-6521-1060-1fcd7865e6ab@gmail.com>
 <952F1896-68C1-4D35-8780-4181F3F80260@sheffield.ac.uk>
 <64ea1a7f-3ea8-74ae-981d-d6daf6eba6bc@gmail.com>
Message-ID: <1cd73dc0-08a2-58c6-e6bf-d28bd2a04a80@gmail.com>

My attempt at a simple HaDec frame and converting ICRS to HA-DEC based 
on icrs_observed.py:

https://gist.github.com/bluthen/8a07259413647b69e045733e97ae9949

It looks like it gives pretty good results. Thank you for the help!


Russell Valentine


On 11/28/20 12:29 PM, Russell Valentine wrote:
> Yes, correct I do want HA-Dec frame.
>
> I had been trying to do that on my own, but it was pretty convoluted. 
> My current procedure was (psudocode):
>
> side_real_time = AltAz(90,0, location, time).to(ICRS).ra
> altaz = my_orig_coord.to(AltAz(location, pressure, time))
> # Make new altaz without pressure and go back to icrs for
> # refraction adjusted ra/dec
> adjusted_icrs = AltAz(altaz.alot, altaz.az, location, time).to(ICRS)
> adjusted_icrs = ICRS(side_real_time - adjusted_icrs.ra, 
> adjusted_icrs.dec)
>
> And then use adjusted_icrs.ra and adjusted_icrs.dec as telescope HA-DEC.
>
> It was not clear to me if the altaz frame took into account 
> precession. Maybe that happens when converting to topocentric CIRS.
>
> Thank you for the reply and suggestion to look at icrs_observed.py I 
> will do that, and try to learn more about these different coordinate 
> systems.
>
>
> Russell Valentine
>
> On 11/28/20 2:53 AM, Stuart P Littlefair wrote:
>> Hi Russel
>>
>> You are correct that TETE does not include atmospheric refraction. 
>> What you want is an HA-Dec frame.
>>
>> It does not exist within astropy yet, but is on the roadmap for the 
>> near future.
>>
>> If you want something to work in the meantime, you could look at the 
>> code in coordinates/builtin_frames/icrs_observed.py in the current 
>> master branch on GitHub.
>>
>> This file contains the transforms from ICRS to AltAz and you will see 
>> that it actually calculates the HA as part of the function!
>>
>> You could simply copy this function and return HA and Dec instead of 
>> Alt and Az.
>>
>> Stuart Littlefair
>> Dept. of Physics & Astronomy
>> Univ. of Sheffield, Sheffield, S3 7RH
>>
>> email: s.littlefair at shef.ac.uk
>> Phone: +44 114 2224525
>> Sent from my iPhone
>>
>>> On 28 Nov 2020, at 06:46, Russell Valentine 
>>> <russell.valentine at gmail.com> wrote:
>>>
>>> ?Thank you for your reply Eric. I do not think TETE can take a 
>>> equinox parameter. I know FK5 has one. I do see what I think is 
>>> precession corrections when I go from ICRS to TETE, however I do not 
>>> think TETE does atmospheric refraction as well.
>>>
>>> https://docs.astropy.org/en/stable/api/astropy.coordinates.builtin_frames.TETE.html#astropy.coordinates.builtin_frames.TETE 
>>>
>>>
>>>
>>>>>> tete = icrs.transform_to(TETE(obstime=t, location=earth_location, 
>>>>>> equinox=t))
>>> Traceback (most recent call last):
>>> ? File "<stdin>", line 1, in <module>
>>> ? File 
>>> "/home/russ/.local/share/virtualenvs/server-zkliv1pZ/lib/python3.7/site-packages/astropy/coordinates/baseframe.py", 
>>> line 609, in __init__
>>> ??? list(kwargs)))
>>> TypeError: Coordinate frame got unexpected keywords: ['equinox']
>>>
>>>
>>>> On 11/27/20 8:24 PM, Eric Jensen wrote:
>>>> Hi Russell,
>>>> I think the thing you?re missing may be the ?equinox? argument to 
>>>> the ?transform_to? call.? I believe that ?obstime? sets the time of 
>>>> your observation for calculating alt/az (and may also be used as 
>>>> the reference date for applying proper motion corrections if you do 
>>>> that), but I don?t think it sets the date for the equinox used for 
>>>> your coordinate system.? Try adding ?equinox=t? to your 
>>>> transformations between ICRS and TETE and see if that helps.??? (I 
>>>> can?t test here because conda channels haven?t caught up with the 
>>>> 4.2 release yet, so I don?t have TETE in my installation.)
>>>> Best,
>>>> Eric
>>>>>> On Nov 27, 2020, at 4:20 PM, Russell Valentine 
>>>>>> <russell.valentine at gmail.com> wrote:
>>>>>
>>>>> Hello,
>>>>>
>>>>> I've been trying to figure out the best way to get correct 
>>>>> coordinates for telescope pointing of a equatorial mount in 
>>>>> astropy. How to, given a set of coordinates in ICRS, convert it to 
>>>>> account for precession and atmosphereic refraction to correctly 
>>>>> move the telescope. It is my understand that you can transform 
>>>>> from ICRS to TETE to compensate for precession, but then how to 
>>>>> also account for atmospheric refraction? I believe the AltAz 
>>>>> coordinate is needed for that.
>>>>>
>>>>> Things I was thinking and tried:
>>>>>
>>>>> 1) ICRS->AltAz (w/pressure)->TETE
>>>>> I do not know if this is correct because you get just very close 
>>>>> to just ICRS. I thought maybe it is right and the refraction just 
>>>>> happens to be the counter the precession, but I tried it on both 
>>>>> east and west horizons with the same result.
>>>>>
>>>>> 2) ICRS->TETE->AltAz(w/pressure)
>>>>>
>>>>> But as expected AltAz is the same as ICRS->AltAz
>>>>>
>>>>> I feel like I am missing some key piece. Has anyone done this with 
>>>>> astropy?
>>>>>
>>>>>
>>>>>
>>>>>
>>>>> from astropy.coordinates import EarthLocation, TETE, ICRS, AltAz, 
>>>>> SkyCoord
>>>>> import astropy.units as u
>>>>> from astropy.time import Time as AstroTime
>>>>> from astropy.units import si as usi
>>>>> t = AstroTime('2020-11-27 19:12:16.894431')
>>>>> earth_location = EarthLocation(lat=38.9369*u.deg, lon= 
>>>>> -95.242*u.deg, height=266.0*u.m)
>>>>> # East horizon object
>>>>> icrs = ICRS(ra=346.23611667*u.deg, dec=12.32287778*u.deg)
>>>>> pressure = 98170.13549857 * u.Pa
>>>>> altaz = icrs.transform_to(AltAz(obstime=t, 
>>>>> location=earth_location, pressure=pressure))
>>>>> tete = icrs.transform_to(TETE(obstime=t, location=earth_location))
>>>>> tete_from_altaz = altaz.transform_to(TETE())
>>>>>
>>>>> # West horizon object
>>>>> icrs2 = ICRS(ra=172.53106667*u.deg, dec=9.27663056*u.deg)
>>>>> altaz2 = icrs2.transform_to(AltAz(obstime=t, 
>>>>> location=earth_location, pressure=pressure))
>>>>> tete2 = icrs2.transform_to(TETE(obstime=t, location=earth_location))
>>>>> tete2_from_altaz2 = altaz2.transform_to(TETE())
>>>>>
>>>>>
>>>>> altaz_from_tete = tete_from_altaz.transform_to(AltAz(obstime=t, 
>>>>> location=earth_location, pressure=pressure))
>>>>> _______________________________________________
>>>>> AstroPy mailing list
>>>>> AstroPy at python.org
>>>>> https://mail.python.org/mailman/listinfo/astropy
>>>> _______________________________________________
>>>> AstroPy mailing list
>>>> AstroPy at python.org
>>>> https://mail.python.org/mailman/listinfo/astropy
>>> _______________________________________________
>>> AstroPy mailing list
>>> AstroPy at python.org
>>> https://mail.python.org/mailman/listinfo/astropy
>> _______________________________________________
>> AstroPy mailing list
>> AstroPy at python.org
>> https://mail.python.org/mailman/listinfo/astropy
>>

From russell.valentine at gmail.com  Mon Nov 30 12:49:16 2020
From: russell.valentine at gmail.com (Russell Valentine)
Date: Mon, 30 Nov 2020 11:49:16 -0600
Subject: [AstroPy] Telescope pointing with astropy,
 atmospheric refraction and precession
In-Reply-To: <1cd73dc0-08a2-58c6-e6bf-d28bd2a04a80@gmail.com>
References: <53fc5305-365d-6521-1060-1fcd7865e6ab@gmail.com>
 <952F1896-68C1-4D35-8780-4181F3F80260@sheffield.ac.uk>
 <64ea1a7f-3ea8-74ae-981d-d6daf6eba6bc@gmail.com>
 <1cd73dc0-08a2-58c6-e6bf-d28bd2a04a80@gmail.com>
Message-ID: <39d87bd9-295d-7b89-9651-a30f12d78108@gmail.com>

https://gist.github.com/bluthen/8a07259413647b69e045733e97ae9949

I also added a function for hadec_to_icrs. Not sure if these conversions 
are valid for all cases but seems to give good results in my limited tests.

I'm excited, thanks again!


Russell Valentine

On 11/29/20 3:37 PM, Russell Valentine wrote:
> My attempt at a simple HaDec frame and converting ICRS to HA-DEC based 
> on icrs_observed.py:
>
> https://gist.github.com/bluthen/8a07259413647b69e045733e97ae9949
>
> It looks like it gives pretty good results. Thank you for the help!
>
>
> Russell Valentine
>
>
> On 11/28/20 12:29 PM, Russell Valentine wrote:
>> Yes, correct I do want HA-Dec frame.
>>
>> I had been trying to do that on my own, but it was pretty convoluted. 
>> My current procedure was (psudocode):
>>
>> side_real_time = AltAz(90,0, location, time).to(ICRS).ra
>> altaz = my_orig_coord.to(AltAz(location, pressure, time))
>> # Make new altaz without pressure and go back to icrs for
>> # refraction adjusted ra/dec
>> adjusted_icrs = AltAz(altaz.alot, altaz.az, location, time).to(ICRS)
>> adjusted_icrs = ICRS(side_real_time - adjusted_icrs.ra, 
>> adjusted_icrs.dec)
>>
>> And then use adjusted_icrs.ra and adjusted_icrs.dec as telescope HA-DEC.
>>
>> It was not clear to me if the altaz frame took into account 
>> precession. Maybe that happens when converting to topocentric CIRS.
>>
>> Thank you for the reply and suggestion to look at icrs_observed.py I 
>> will do that, and try to learn more about these different coordinate 
>> systems.
>>
>>
>> Russell Valentine
>>
>> On 11/28/20 2:53 AM, Stuart P Littlefair wrote:
>>> Hi Russel
>>>
>>> You are correct that TETE does not include atmospheric refraction. 
>>> What you want is an HA-Dec frame.
>>>
>>> It does not exist within astropy yet, but is on the roadmap for the 
>>> near future.
>>>
>>> If you want something to work in the meantime, you could look at the 
>>> code in coordinates/builtin_frames/icrs_observed.py in the current 
>>> master branch on GitHub.
>>>
>>> This file contains the transforms from ICRS to AltAz and you will 
>>> see that it actually calculates the HA as part of the function!
>>>
>>> You could simply copy this function and return HA and Dec instead of 
>>> Alt and Az.
>>>
>>> Stuart Littlefair
>>> Dept. of Physics & Astronomy
>>> Univ. of Sheffield, Sheffield, S3 7RH
>>>
>>> email: s.littlefair at shef.ac.uk
>>> Phone: +44 114 2224525
>>> Sent from my iPhone
>>>
>>>> On 28 Nov 2020, at 06:46, Russell Valentine 
>>>> <russell.valentine at gmail.com> wrote:
>>>>
>>>> ?Thank you for your reply Eric. I do not think TETE can take a 
>>>> equinox parameter. I know FK5 has one. I do see what I think is 
>>>> precession corrections when I go from ICRS to TETE, however I do 
>>>> not think TETE does atmospheric refraction as well.
>>>>
>>>> https://docs.astropy.org/en/stable/api/astropy.coordinates.builtin_frames.TETE.html#astropy.coordinates.builtin_frames.TETE 
>>>>
>>>>
>>>>
>>>>>>> tete = icrs.transform_to(TETE(obstime=t, 
>>>>>>> location=earth_location, equinox=t))
>>>> Traceback (most recent call last):
>>>> ? File "<stdin>", line 1, in <module>
>>>> ? File 
>>>> "/home/russ/.local/share/virtualenvs/server-zkliv1pZ/lib/python3.7/site-packages/astropy/coordinates/baseframe.py", 
>>>> line 609, in __init__
>>>> ??? list(kwargs)))
>>>> TypeError: Coordinate frame got unexpected keywords: ['equinox']
>>>>
>>>>
>>>>> On 11/27/20 8:24 PM, Eric Jensen wrote:
>>>>> Hi Russell,
>>>>> I think the thing you?re missing may be the ?equinox? argument to 
>>>>> the ?transform_to? call.? I believe that ?obstime? sets the time 
>>>>> of your observation for calculating alt/az (and may also be used 
>>>>> as the reference date for applying proper motion corrections if 
>>>>> you do that), but I don?t think it sets the date for the equinox 
>>>>> used for your coordinate system.? Try adding ?equinox=t? to your 
>>>>> transformations between ICRS and TETE and see if that helps.??? (I 
>>>>> can?t test here because conda channels haven?t caught up with the 
>>>>> 4.2 release yet, so I don?t have TETE in my installation.)
>>>>> Best,
>>>>> Eric
>>>>>>> On Nov 27, 2020, at 4:20 PM, Russell Valentine 
>>>>>>> <russell.valentine at gmail.com> wrote:
>>>>>>
>>>>>> Hello,
>>>>>>
>>>>>> I've been trying to figure out the best way to get correct 
>>>>>> coordinates for telescope pointing of a equatorial mount in 
>>>>>> astropy. How to, given a set of coordinates in ICRS, convert it 
>>>>>> to account for precession and atmosphereic refraction to 
>>>>>> correctly move the telescope. It is my understand that you can 
>>>>>> transform from ICRS to TETE to compensate for precession, but 
>>>>>> then how to also account for atmospheric refraction? I believe 
>>>>>> the AltAz coordinate is needed for that.
>>>>>>
>>>>>> Things I was thinking and tried:
>>>>>>
>>>>>> 1) ICRS->AltAz (w/pressure)->TETE
>>>>>> I do not know if this is correct because you get just very close 
>>>>>> to just ICRS. I thought maybe it is right and the refraction just 
>>>>>> happens to be the counter the precession, but I tried it on both 
>>>>>> east and west horizons with the same result.
>>>>>>
>>>>>> 2) ICRS->TETE->AltAz(w/pressure)
>>>>>>
>>>>>> But as expected AltAz is the same as ICRS->AltAz
>>>>>>
>>>>>> I feel like I am missing some key piece. Has anyone done this 
>>>>>> with astropy?
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>> from astropy.coordinates import EarthLocation, TETE, ICRS, AltAz, 
>>>>>> SkyCoord
>>>>>> import astropy.units as u
>>>>>> from astropy.time import Time as AstroTime
>>>>>> from astropy.units import si as usi
>>>>>> t = AstroTime('2020-11-27 19:12:16.894431')
>>>>>> earth_location = EarthLocation(lat=38.9369*u.deg, lon= 
>>>>>> -95.242*u.deg, height=266.0*u.m)
>>>>>> # East horizon object
>>>>>> icrs = ICRS(ra=346.23611667*u.deg, dec=12.32287778*u.deg)
>>>>>> pressure = 98170.13549857 * u.Pa
>>>>>> altaz = icrs.transform_to(AltAz(obstime=t, 
>>>>>> location=earth_location, pressure=pressure))
>>>>>> tete = icrs.transform_to(TETE(obstime=t, location=earth_location))
>>>>>> tete_from_altaz = altaz.transform_to(TETE())
>>>>>>
>>>>>> # West horizon object
>>>>>> icrs2 = ICRS(ra=172.53106667*u.deg, dec=9.27663056*u.deg)
>>>>>> altaz2 = icrs2.transform_to(AltAz(obstime=t, 
>>>>>> location=earth_location, pressure=pressure))
>>>>>> tete2 = icrs2.transform_to(TETE(obstime=t, location=earth_location))
>>>>>> tete2_from_altaz2 = altaz2.transform_to(TETE())
>>>>>>
>>>>>>
>>>>>> altaz_from_tete = tete_from_altaz.transform_to(AltAz(obstime=t, 
>>>>>> location=earth_location, pressure=pressure))
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From tony.willis.research at gmail.com  Mon Nov 30 20:02:25 2020
From: tony.willis.research at gmail.com (Tony Willis)
Date: Mon, 30 Nov 2020 17:02:25 -0800
Subject: [AstroPy] Telescope pointing with astropy,
 atmospheric refraction, and precession
Message-ID: <1e3d5d5b-4b29-7bdf-bd2e-4049d5541b8d@gmail.com>

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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