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dstndstn / astrometry.net

Astrometry.net -- automatic recognition of astronomical images
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Measure FWHM of detected sources #73

Open dstndstn opened 8 years ago

dstndstn commented 8 years ago

requested by Roberto Abraham

AndrewBuck commented 7 years ago

I'm not sure what the original reason that the FWHM was asked to be measured, however I have been thinking about how to speed up the solving algorithm and it occurred to me FWHM could be used.

Since you can make a rough estimate that the FWHM is probably a few arcseconds across, the measured value gives you some rough estimate of the pixel scale of the image. So for images where no pixel scale estimate is given on the command line, you could look at the FWHM of stars in the image and use that to check catalogs in the appropriate sizes first.

dstndstn commented 7 years ago

interesting idea! I would guess, though, that for a lot of the images we get (eg, backyard snapshots with fairly wide-angle cameras), the FWHM of stars is due mostly to optics or defocus, rather than seeing.