APOD: The Tarantula Zone (2020 Nov 13)

Comments and questions about the APOD on the main view screen.
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Chris Peterson
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Re: APOD: The Tarantula Zone (2020 Nov 13)

Post by Chris Peterson » Sun Nov 15, 2020 5:06 am

alter-ego wrote:
Sun Nov 15, 2020 4:54 am
johnnydeep wrote:
Sat Nov 14, 2020 10:21 pm
Chris Peterson wrote:
Sat Nov 14, 2020 7:51 pm


It can be done inside some image processing programs (this image was processed with PixInsight, which has a plate solving tool). It can also be done by uploading an image to Astrometry.net, which can solve almost anything. This image has almost all the stars processed out, by virtue of so much signal coming from a very narrow H-alpha and OIII channels. But there were probably enough stars in the unprocessed frames to get a solution. It's also easy enough to just solve a clean star field, which will give you the pixel scale for a given imaging train, and just use that value, multiplied by the number of pixels on an axis.
Neat!
There's more than enough visible detail to determine the field by eye when overlapping images. Having an FOV [X,Y] error of [10",6"], the visually dialed-in DSS2 image with the APOD image is shown in the hover-image below. I normally don't attempt that level of precision, but I was curious how well I could measure the FOV given Ignacio's stated dimensions.
We should note, however, that a proper plate solution goes well beyond providing the FOV. It identifies the center of the plate to a fraction of a pixel, as well as a set of mathematical coefficients that describe rotation and a number of different mapping distortions. Using the values generated by the plate solution, the astrometric position (RA and declination) of any star or structure in the image can be calculated with sub-pixel accuracy.
Chris

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alter-ego
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Re: APOD: The Tarantula Zone (2020 Nov 13)

Post by alter-ego » Sun Nov 15, 2020 5:15 am

Chris Peterson wrote:
Sun Nov 15, 2020 5:06 am
alter-ego wrote:
Sun Nov 15, 2020 4:54 am
johnnydeep wrote:
Sat Nov 14, 2020 10:21 pm

Neat!
There's more than enough visible detail to determine the field by eye when overlapping images. Having an FOV [X,Y] error of [10",6"], the visually dialed-in DSS2 image with the APOD image is shown in the hover-image below. I normally don't attempt that level of precision, but I was curious how well I could measure the FOV given Ignacio's stated dimensions.
We should note, however, that a proper plate solution goes well beyond providing the FOV. It identifies the center of the plate to a fraction of a pixel, as well as a set of mathematical coefficients that describe rotation and a number of different mapping distortions. Using the values generated by the plate solution, the astrometric position (RA and declination) of any star or structure in the image can be calculated with sub-pixel accuracy.
Yeah, no doubt is a powerful tool. Although I've not needed that analysis power myself, I have to admit it occasionally might save me some time. :)
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