I'm wondering if there can't be a user defined setting where if the sun is below a threshold altitude, the time is considered past twilight. I know this is an odd request, but standard astronomical dusk requires the sun to be below 18 degrees from below the horizon. Some locations for imaging have skies brighter than true dark sites, so the sky gets as dark as it can well before the sun gets to -18 degrees. This is also the case w/ the moon up.

Also, you can cheat a bit and image in narrowband filters before the sun gets to -18 degrees. This adds up and allows for a bit more imaging time.

Gabe

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