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Re: GMT from Lunar Photo
From: Peter Monta
Date: 2022 Jan 07, 20:36 +0000
From: Peter Monta
Date: 2022 Jan 07, 20:36 +0000
The star at one-o'clock that's just about to be occulted is HD 202635 (magnitude 8.7).
Attached is an overlay consisting of white dots where the stars are. Feeding this to astrometry.net's "solve-field" (or the on-line service at nova.astrometry.net) gives:
Field: espenak-stars.png
Field center: (RA,Dec) = (319.246330, -21.483549) deg.
Field center: (RA H:M:S, Dec D:M:S) = (21:16:59.119, -21:29:00.778).
Field size: 71.7088 x 47.9776 arcminutes
Field rotation angle: up is -124.758 degrees E of N
Plate scale is 2.691 arcsec/pixel.
So the stars have done their job, and every pixel in the image now has RA and Dec coordinates. The next step is to find the pixel coordinates of the Moon's center of mass, which can then be immediately translated to RA,Dec. Picking points along the dim limb and fitting a circle (or ellipse) would be one way to go.
My initial reaction to the star on the limb was "a pity, that one can't be used because both sides of the trail are not clearly seen". One man's trash is another's treasure I guess---certainly just using the available occultation tools directly is a valid path.
Cheers,
Peter
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