Is there a way to increase the number of labeled stars, or to superimpose a grid for declination and RA?

28 views
Skip to first unread message

James van Scoyoc

unread,
Jun 9, 2022, 8:28:50 PMJun 9
to astrometry
I use nova.astrometry.net mainly to test my astrophotography exposures and post-processing work.  I want to find the faintest stars my sensor can pick up given the compromised observing conditions I usually work under.  I also want to be sure that no high-ISO-generated noise pixels are being incorrectly identified as stars by the Photoshop filters I use prior to Astrometry.

When I have the results from Astrometry, my usual procedure is to open up my favorite stargazing app and compare the map to my image.  But at any given time I can only look at one of those things, and I don't really have a way to look at them side-by-side.  Moreover, stargazing apps generally don't let you rotate the display at will, so you can't orient the map image to in the same position as the photo.

One thing that would help would be if I could increase the number of stars that are labeled, or if I could indicate particular stars that I wanted to have labeled.

Even better would be a way to superimpose a grid for RA and declination, appropriate to the size of the image.  Is there a way to do that?

Dustin Lang

unread,
Jun 10, 2022, 8:09:14 AMJun 10
to James van Scoyoc, astrometry
Hi,

If you have the ability to run the "plotann.py" script from the Astrometry.net code (this requires building the whole codebase), then that is a fairly versatile tool.  You can mark an object of your choosing with "--target-rd MyStar 43.24 7.64" to label at a given RA,Dec.  You can set the RA,Dec grid size with "--grid-size 0.25" for 1/4-degree increments.

cheers,
dustin


--
You received this message because you are subscribed to the Google Groups "astrometry" group.
To unsubscribe from this group and stop receiving emails from it, send an email to astrometry+...@googlegroups.com.
To view this discussion on the web visit https://groups.google.com/d/msgid/astrometry/db9c3c25-d1a1-4777-b89a-10672758767cn%40googlegroups.com.
Message has been deleted

paul.l...@gmail.com

unread,
Jun 10, 2022, 9:52:30 AMJun 10
to astrometry

Possibly overkill for your purposes, but you could use a real photomety program (I use APT, some swear by or at Astrometrica) and get precise values for the limiting magnitude of visible stars and an estimate of the sky brightness in magnitudes per square arcsecond.

Dustin Lang

unread,
Jun 10, 2022, 10:00:20 AMJun 10
to paul.l...@gmail.com, astrometry
Way back when, we experimented with doing photometric calibration using the Astrometry.net results also -- it worked pretty well, and you could also guess what the filter was.


--
You received this message because you are subscribed to the Google Groups "astrometry" group.
To unsubscribe from this group and stop receiving emails from it, send an email to astrometry+...@googlegroups.com.

Bryan

unread,
Jun 10, 2022, 11:50:44 PMJun 10
to astrometry
" Moreover, stargazing apps generally don't let you rotate the display at will, so you can't orient the map image to in the same position as the photo."

I do this with Cartes du Ciel.  You can rotate the image in 15d increments.

Bryan
Reply all
Reply to author
Forward
0 new messages