Mailman 3 ডিসেম্বর 2020 - AstroPy

consistency of reference frames between SkyCoord and JPL Horizons
by Paolo Tanga 27 জানুয়ারি, 2021

27 জানুয়ারি, 2021

Hi all I am trying to plug the results by JPL Horizons into the appropriate reference system of a SkyCoord object, but it looks very trick. (bewore long message, I hope the explanation is clear for the specialists of reference systems) The Horizons server returns two types of equatorial coordinates: "astrometric" (1) and (2) "apparent". Their description is the following: - (1): astrometric RA and Dec with respect to the observing site (coordinate origin) in the reference frame of the planetary ephemeris (ICRF). Compensated for down-leg light-time delay aberration. - (2): Airless apparent RA and Dec of the target with respect to an instantaneous reference frame defined by the Earth equator of-date (z-axis) and meridian containing the Earth equinox of-date (x-axis, IAU76/80). Compensated for down-leg light-time delay, gravitational deflection of light, stellar aberration, precession & nutation. Note: equinox (RA origin) is offset -53 mas from the of-date frame defined by the IAU06/00a P & N system. My guess is none of these two systems correspond to either ICRS or GCRS as defined in astropy. The simplest possibility for me, would have been to assimilate (1), computed for the Solar System barycenter, to ICRS. But definitely (2) is not GCRS and the test below easily proves that. Verification (see the attached notebook if you want to play with) : - I queried for Solar System barycentric coordinates (1) of an asteroid at one epoch. I inserted them in a SkyCoord object as ICRS and use the transform_to(GCRS) towards geocentric, at the given epoch. - I queried again JPL Horizons for the apparent coordinates (2) from the geocenter, directly. As expected, by comparing the results I get the patent confirmation that GCRS is not the frame of (2), with a discrepancy of 16 arcmin in my case. SO, IT DOES NOT WORK, AS EXPECTED. Let's put apparent coordinates (2) aside for the moment. Second possibility (see notebook again). I take coordinates (1), for the geocentric observer. I insert them as GCRS in a SkyCoord object. I trasform_to(ICRS) (barycentric observer) and compare the result to a query of (1) directly for the barycentric observer. Again this SHOULD NOT WORK accurately. In fact the definition of (1) does not contain annual aberration and light deflection that are part of GCRS. A difference of several arcsec (mostly due to annual aberration) SHOULD show up. And in fact IT DOES, ~8 arcsec of difference. The conclusions if that using SkyCoord with the output of JPL Horizons is far from obvious to the end user... ---- So, my final questions/remarks are: - How to get a fully accurate consistency between a SkyCoord frame and JPL Horizons output, in the case of a barycentric, geocentric or topocentric observer, for both "astrometric" and "apparent" coordinates as provided by JPL? Which reference SkyCoord should use and how? - Does astropy implement GCRS correctly in the case of Solar System objects, by taking into account aberration and light deflection in the relativistic form, for an object at finite distance (different than for the stars!) ? - ...or... Am I missing something fundamental in my interpretation? - Eventually, this query to Horizons turns our to be tricky to manage as SkyCoord for the final user. I think it would be useful to provide the correct recipe and/or directly a SkyCoord as output of the query... Best regards Paolo -- --------------------------------------------------------------------- Paolo Tanga Astronomer Deputy director of Laboratoire Langrange / UMR 7293 Observatoire de la Côte d'Azur Tel +33(0)492003042 Bv de l'Observatoire - CS 34229 Fax +33(0)492003121 06304 Nice Cedex 4 - France http://www.oca.eu/tanga https://twitter.com/ziggypao

2 1

Reading/writing tables
by Judith Irwin 9 ডিসেম্বর, 2020

9 ডিসেম্বর, 2020

Could someone help with this problem? I want to read a fits table and write out a .csv file. Here is what I'm doing: >>> import astropy >>> from astropy.table import Table >>> from astropy.io import ascii >>> t=Table.read('merged_0.3-7_newerr_src.fits') >>> print t RA DEC RA_ERR DEC_ERR X ... 797_OFFAXS_ANG WEIGHT_OFFAXS WANG_ERR POS_ERR deg deg deg deg pix ... arcmin arcmin arcmin arcmin ------------- ------------- ----------------- ----------------- ------------- ... -------------- -------------- ---------------- ---------------- 190.491776756 32.4809974381 7.81833679753e-06 4.8707159408e-06 4071.66367713 ... 2.958585048 2.958585048 0.00652461345853 0.00654797997354 190.490783106 32.4956819235 2.04948640032e-05 3.86556461152e-05 4077.8 ... 2.07617011778 2.07617011778 0.00490486335967 0.00556319682508 (I'm only showing the first rows of the table) >>> ascii.write(t, 'Xsources_new.csv', format='csv',overwrite=True) Traceback (most recent call last): File "<stdin>", line 1, in <module> File "/home/irwin/.local/lib/python2.7/site-packages/astropy/io/ascii/ui.py", line 733, in write writer.write(table, output) File "/home/irwin/.local/lib/python2.7/site-packages/astropy/io/ascii/fastbasic.py", line 179, in write self._write(table, output, {'fill_values': [(core.masked, '')]}) File "/home/irwin/.local/lib/python2.7/site-packages/astropy/io/ascii/fastbasic.py", line 156, in _write writer.write(output, header_output, output_types) File "astropy/io/ascii/cparser.pyx", line 1036, in astropy.io.ascii.cparser.FastWriter.write TypeError: unhashable type: 'list' >>> ascii.write(t, 'Xsources_new.csv', format='csv',overwrite=True,comment=False) Traceback (most recent call last): File "<stdin>", line 1, in <module> File "/home/irwin/.local/lib/python2.7/site-packages/astropy/io/ascii/ui.py", line 733, in write writer.write(table, output) File "/home/irwin/.local/lib/python2.7/site-packages/astropy/io/ascii/fastbasic.py", line 179, in write self._write(table, output, {'fill_values': [(core.masked, '')]}) File "/home/irwin/.local/lib/python2.7/site-packages/astropy/io/ascii/fastbasic.py", line 156, in _write writer.write(output, header_output, output_types) File "astropy/io/ascii/cparser.pyx", line 1036, in astropy.io.ascii.cparser.FastWriter.write TypeError: unhashable type: 'list' I also tried comment=False in the write statement. I include the input file as an attachment. Thanks. Judith

6 8

ANN: Astropy v4.2 and v4.0.4 releases
by Brigitta Sipocz 7 ডিসেম্বর, 2020

7 ডিসেম্বর, 2020

Dear All, On behalf of the Astropy Project, I am pleased to announce the v4.2 release of astropy, the core Python package for astronomy. This astropy release supports Python 3.7-3.9 and Numpy 1.17+. This release includes new functionalities, fixes and improvements for 183 issues, 105 pull requests, from 63 contributors. An overview is provided at this page: https://docs.astropy.org/en/stable/whatsnew/4.2.html For a full list of the changes, please consult the Changelog: https://docs.astropy.org/en/stable/changelog.html#changelog To install the new version you can either use pip: pip install astropy --upgrade Or if you are a user of Anaconda, the new version is available both on their default channel, or on the conda-forge one: conda update astropy Extensive user documentation of Astropy can be found on our website: http://docs.astropy.org Along with this new feature release, we have also released v4.0.4 for the long term support (LTS) branch. This LTS branch will be maintained and receive regular bugfix releases until the autumn of 2021. If you use Astropy directly for your work, or as a dependency to another package, please remember to acknowledge it by citing the appropriate Astropy paper. For the most up-to-date suggestions, see the acknowledgement page: https://www.astropy.org/acknowledging.html : This research made use of Astropy, a community-developed core Python package for Astronomy (Astropy Collaboration, 2018). As always, please report any issues or problems to our GitHub repository: https://github.com/astropy/astropy/issues A big thank you to everybody who contributed! All the best, Brigitta Sipőcz

1 0

Re: [AstroPy] Telescope pointing with astropy, atmospheric, refraction, and precession
by Tony Willis 3 ডিসেম্বর, 2020

3 ডিসেম্বর, 2020

Hi Stuart As you requested, I'm attaching the output from that script I posted. Cheers Tony On 2020-12-02 9:00 a.m., astropy-request(a)python.org wrote: > Send AstroPy mailing list submissions to > astropy(a)python.org > > To subscribe or unsubscribe via the World Wide Web, visit > https://mail.python.org/mailman/listinfo/astropy > or, via email, send a message with subject or body 'help' to > astropy-request(a)python.org > > You can reach the person managing the list at > astropy-owner(a)python.org > > When replying, please edit your Subject line so it is more specific > than "Re: Contents of AstroPy digest..." > > > Today's Topics: > > 1. Re: AstroPy Digest, Vol 171, Issue 1 (Tony Willis) > 2. Re: AstroPy Digest, Vol 171, Issue 1 (Stuart P Littlefair) > > > ---------------------------------------------------------------------- > > Message: 1 > Date: Tue, 1 Dec 2020 09:57:37 -0800 > From: Tony Willis <tony.willis.research(a)gmail.com> > To: astropy(a)python.org > Subject: Re: [AstroPy] AstroPy Digest, Vol 171, Issue 1 > Message-ID: <60e9e251-6825-55a8-63f1-ea6aae068aa2(a)gmail.com> > Content-Type: text/plain; charset=utf-8; format=flowed > > Hi Stuart > > Sure - tell me exactly what you would like done. > > Tony > > On 2020-12-01 9:00 a.m., astropy-request(a)python.org wrote: >> Send AstroPy mailing list submissions to >> astropy(a)python.org >> >> To subscribe or unsubscribe via the World Wide Web, visit >> https://mail.python.org/mailman/listinfo/astropy >> or, via email, send a message with subject or body 'help' to >> astropy-request(a)python.org >> >> You can reach the person managing the list at >> astropy-owner(a)python.org >> >> When replying, please edit your Subject line so it is more specific >> than "Re: Contents of AstroPy digest..." >> >> >> Today's Topics: >> >> 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(a)sheffield.ac.uk> >> To: Astronomical Python mailing list <astropy(a)python.org> >> Subject: Re: [AstroPy] Telescope pointing with astropy, atmospheric >> refraction, and precession >> Message-ID: >> <CAOrDc-9JOPrd9fAhfEr5Uwd5J_v07O-iu5b1EdNEER0uGoGPgg(a)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(a)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 >>> >>> _______________________________________________ >>> AstroPy mailing list >>> AstroPy(a)python.org >>> https://mail.python.org/mailman/listinfo/astropy >>> > > ------------------------------ > > Message: 2 > Date: Tue, 1 Dec 2020 22:09:42 +0000 > From: Stuart P Littlefair <s.littlefair(a)sheffield.ac.uk> > To: Astronomical Python mailing list <astropy(a)python.org> > Subject: Re: [AstroPy] AstroPy Digest, Vol 171, Issue 1 > Message-ID: > <CAOrDc-9Yyx3cqG+a0mhBYr_tLzsTBzzZNwrRjSj9LKNzbwLctA(a)mail.gmail.com> > Content-Type: text/plain; charset="utf-8" > > Thanks Tony, > > If you could just post the output of the script you attached, to save me > from installing CASA tools, that would be great! > > Stuart > > On Tue, 1 Dec 2020 at 17:58, Tony Willis <tony.willis.research(a)gmail.com> > wrote: > >> Hi Stuart >> >> Sure - tell me exactly what you would like done. >> >> Tony >> >> On 2020-12-01 9:00 a.m., astropy-request(a)python.org wrote: >>> Send AstroPy mailing list submissions to >>> astropy(a)python.org >>> >>> To subscribe or unsubscribe via the World Wide Web, visit >>> https://mail.python.org/mailman/listinfo/astropy >>> or, via email, send a message with subject or body 'help' to >>> astropy-request(a)python.org >>> >>> You can reach the person managing the list at >>> astropy-owner(a)python.org >>> >>> When replying, please edit your Subject line so it is more specific >>> than "Re: Contents of AstroPy digest..." >>> >>> >>> Today's Topics: >>> >>> 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(a)sheffield.ac.uk> >>> To: Astronomical Python mailing list <astropy(a)python.org> >>> Subject: Re: [AstroPy] Telescope pointing with astropy, atmospheric >>> refraction, and precession >>> Message-ID: >>> < >> CAOrDc-9JOPrd9fAhfEr5Uwd5J_v07O-iu5b1EdNEER0uGoGPgg(a)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(a)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 >>>> >>>> _______________________________________________ >>>> AstroPy mailing list >>>> AstroPy(a)python.org >>>> https://mail.python.org/mailman/listinfo/astropy >>>> >> _______________________________________________ >> AstroPy mailing list >> AstroPy(a)python.org >> https://mail.python.org/mailman/listinfo/astropy >> >

1 0

sigma filter in astropy
by Al va 3 ডিসেম্বর, 2020

3 ডিসেম্বর, 2020

Hi I have this function in IDL that compares the value of each pixel with the mean of the box around it and if the value of the pixel is bigger than the mean plus 3sigma it is replaced by the mean of the box. Is there any function in astropy doing something similar to that? Thanks!

1 0

Re: [AstroPy] AstroPy Digest, Vol 171, Issue 1
by Tony Willis 1 ডিসেম্বর, 2020

1 ডিসেম্বর, 2020

Hi Stuart Sure - tell me exactly what you would like done. Tony On 2020-12-01 9:00 a.m., astropy-request(a)python.org wrote: > Send AstroPy mailing list submissions to > astropy(a)python.org > > To subscribe or unsubscribe via the World Wide Web, visit > https://mail.python.org/mailman/listinfo/astropy > or, via email, send a message with subject or body 'help' to > astropy-request(a)python.org > > You can reach the person managing the list at > astropy-owner(a)python.org > > When replying, please edit your Subject line so it is more specific > than "Re: Contents of AstroPy digest..." > > > Today's Topics: > > 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(a)sheffield.ac.uk> > To: Astronomical Python mailing list <astropy(a)python.org> > Subject: Re: [AstroPy] Telescope pointing with astropy, atmospheric > refraction, and precession > Message-ID: > <CAOrDc-9JOPrd9fAhfEr5Uwd5J_v07O-iu5b1EdNEER0uGoGPgg(a)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(a)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 >> >> _______________________________________________ >> AstroPy mailing list >> AstroPy(a)python.org >> https://mail.python.org/mailman/listinfo/astropy >> >

2 1

Re: [AstroPy] Telescope pointing with astropy, atmospheric refraction, and precession
by Tony Willis 1 ডিসেম্বর, 2020

1 ডিসেম্বর, 2020

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

2 1