[AstroPy] Using Astropy to plot skymaps...possible error in tutorial?

Kelle Cruz kellecruz at gmail.com
Mon Dec 9 12:25:31 EST 2019

Hi Tom,

Cool, glad to hear that tutorial is useful! And this tweak to the tutorial
would be very welcome! As far as I know, I don't think there is a
convention and I think pointing out that folks may want to think
deliberately about which way to do it is useful.

Please consider posting an issue here in the tutorials repo:

If you wanted to make the tweak yourself, that would also be amazing. You
could fork the repo and modify the notebook or download it and edit it in
Google Colab and then share it with us. Both methods are described in the
Contributor instructions:

And notebook is here:


Kelle Cruz, PhD
917.837.9748 — Hunter: x16486 — AMNH: x7930
Pronouns: she/her and they/them

On Mon, Dec 9, 2019 at 12:15 PM William Bridgman <wtbsvs at gmail.com> wrote:

> I occasionally need to generate reference charts and plots for some of
> my work producing content for general audiences and I was trying to
> use the charting tutorial at the bottom of
> http://learn.astropy.org/rst-tutorials/plot-catalog.html
> However, if I plot the Yale Bright star catalog using this algorithm,
> I get unrecognizable constellations.
> ra,dec,magnitude = YaleStars.ExtractBasic()
> coords_icrs = coord.SkyCoord(ra,dec,frame='icrs')
> fig = plt.figure(figsize=(8,4.5))
> axes = fig.add_subplot(111,projection='mollweide')
> axes.scatter(ra.radian, dec.radian,s=(vMagThreshold - magnitude+1)**2)
> axes.set_xticklabels(['14h','16h','18h','20h', '22h', '0h',
> '2h','4h','6h','8h','10h'])
> axes.grid(True)
> plt.show()
> Checking against my reference charts clearly shows the constellations
> reversed (see ICRSflipped.pdf).
> A change to the above fixed this issue (ICRS.pdf):
> axes.scatter(-ra.radian, dec.radian,s=(vMagThreshold - magnitude+1)**2)
> axes.set_xticklabels(['10h','8h','6h','4h', '2h', '0h',
> '22h','20h','18h','16h','14h'])
> Is there a legitimate convention for plotting skymaps reversed,
> perhaps to match instrument view?
> What's the procedure for revising tutorials?
> Thanks,
> Tom
> --
> Dr. William T."Tom" Bridgman
> Scientific Visualization Studio
> NASA/Goddard Space Flight Center
> Greenbelt, MD  20771
> http://svs.gsfc.nasa.gov
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> AstroPy mailing list
> AstroPy at python.org
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