How to access the star positions (stars by magnitude within FoV)?

[andreas....@gmail.com]

Hi there,

I am trying to optically find satellites within images. That works okay-ish already[0]

It would help me to get the star positions from Astrometry. So far I did not find an option or standarf output for it.

The reason is, that one of my processing steps of the optical search is to find the center of the satellite dot. Due to the fact it is also starlike and faint, the gaussian kernel [3x3] is finding the satellite dot within the search window. But when there is a real star or other britghter object inside, the kernel is "sucked" to it and is finding this star instead of the satellite.

So what I am trying to do now is to filter out the known stars inside the image before searching for the satellite dots. So it would be great to have access to the stars and their magnitudes from the Astrometry output.

maybe someone also did this already :). Would be great to know how this could work.

[0] https://www.youtube.com/watch?v=jV9u9WspsI4

[1] https://aerospaceresearch.net/?page_id=2310

Best regards,

Andreas

[Dustin Lang]

Are you using the nova.astrometry.net web service, or the solve-field program?  Either way, the known stars are in "rdls" files (RA,Dec lists), and "stars" detected in your image are in "xy" or "axy" or "xyls" files.  (Both of these are just binary FITS table format.)

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[paul.l...@gmail.com]

Heresy, perhaps, but have you tried Astrometrica? It is specifically designed to perform astrometry and photometry of moving objects.

[Andreas Hornig]

Hi Dustin,

thanks for your answer.

On Sat, Aug 21, 2021 at 1:46 PM Dustin Lang <dstn...@gmail.com> wrote:

Are you using the nova.astrometry.net web service, or the solve-field program?  Either way, the known stars are in "rdls" files (RA,Dec lists), and "stars" detected in your image are in "xy" or "axy" or "xyls" files.  (Both of these are just binary FITS table format.)

I am using Astrometry on my raspberry pi, but not the api to nova.

ah, okay, then I need to check these files. I haven't done that so far. Let me see how the format is and which stars were detected and which additional stars I can take from the catalogue.

Andreas 

[Andreas Hornig]

Hi Paul.

On Sat, Aug 21, 2021 at 3:30 PM paul.l...@gmail.com <paul.l...@gmail.com> wrote:

Heresy, perhaps, but have you tried Astrometrica? It is specifically designed to perform astrometry and photometry of moving objects.

heresy in the name of which heavenly church? :)

Jokes beside, no, I haven't tried Astrometrica. Now I need to check if it serves my purpose of detecting satellites and putting out the ra-dec-timestamp.

thanks for the tipp.

Andreas

[Dustin Lang]

The "tablist" program in the Astrometry.net package will print them out for you.  The solve-field program produces the file X.rdls which contains the RA,Dec positions of reference (known) stars.  (Not all known stars, but those that appeared in the index files.)  The X.corr file contains "correspondences" -- reference stars near stars detected in your image, with X,Y,RA,Dec positions.  The X.axy file contains the pixel positions of sources detected in your image.  You can use wcs-rd2xy and wcs-xy2rd programs to convert between X,Y and RA,Dec lists.

cheers,

--dustin