A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Frank Reed
Date: 2021 Dec 20, 17:16 -0800
David Pike, you wrote:
"3. Betelgeuse is about level with Sirius and lowish in the east."
Yes, Sirius is perhaps a degree higher. And below Canopus is Avior, which is maybe a degree higher still than Sirius. So suppose we say that the altitude of Sirius is 20°+x. That puts Betelgeuse at around 19°+x, and Avior near 21°+x. This becomes a three-body fix with an unknown altitude correction, like when we don't know the correct dip. So even without knowing that Sirius is really 15° or 20° or 25° high, the fact that we can estimate roughly that the other stars are a degree higher and a degree lower should be enough to get an approximate fix, right? If we're limited to two stars, that doesn't work. But with three, we can force a fix.
"and there are streetlights on, so it’s probably dark outside."
I don't see any streetlights, but it's certainly an oddly "bright" scene. The sky itself is bright, and there's an over-exposed "glint" on the dome below Sirius and Rigel. Where's that coming from? And more importantly, what the heck is this owl doing out in the middle of the night over two hours before civil twilight?! This is not his usual perching spot obviously, so that means he was flying, presumably hunting, shortly before the image was taken. Why so bright? Why is an owl hunting? The answer I think is hiding behind those fluffy feathers in the part of the sky directly opposite Sirius which we can't see. It's the Full Moon. In fact, the timestamp tells us that it's only about two hours before the exact time of the Full Moon (as usually defined) on this date. So this landscape is indeed brightly lit, and it's a great time to be an owl on the prowl...