NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Frank Reed
Date: 2023 Nov 30, 08:09 -0800
Bill Ritchie, you wrote:
"I enjoyed seeing the nearly full Moon in the NW around 0800 on Tuesday morning. It was about ten Moon diameters above the horizon and almost exactly over the distant TV mast behind which the Sun sets on mid summer’s day. That fits in with the 5° tilt that you highlight."
Glad you got to see it. I drove over to the local beach a few minutes ago and caught the faintly visible upper half of the Moon approaching the low hills on the mainland northwest of here. So I saw it a few minutes after moonrise at 18:00 local time yesterday evening and again just above the horizon at 10:00 this morning. The Moon has had a long night!
You added:
"The opposing Southern hemisphere location would show two Moon sets within 24 hours. What happened to the sailor’s “50 minutes later every day” adage?"
Well, what do you make of the definitional problem for moonrise and moonset "today"? Do I mean today by the civil day or something else? I still find this problematic after decades of dealing with it.
You also wrote:
"Of more direct navigation interest, imagine taking Moon meridian passage sights with an accurate theodolite, recording the time of culmination and calculating your latitude and longitude. [...] Perhaps using the Moon for meridian passage sights is not always a good idea. "
Heh. Funny you should mention that! We can fix this. I'm sure if any of our math-y contributors ponder it for a while, we'll see several ways to do it. It's not so different from a vessel sailing due south at some speed while taking sights around local noon. The maximum altitude gets skewed substantially to the right, but it's a correctable error. I have been working on some enhancements for Moon variations on this principle, and it happens to be on my "to do" schedule for next week. I'm sharing a little screenshot of my schedule spreadsheet here, both for the entertainment of the group, and so you can see that I'm being literal when I say it's on my schedule for next week! Then again, it was on my schedule last week, too. Somehow it keeps slipping through the cracks in those spreadsheet cells...
Frank Reed
Clockwork Mapping / ReedNavigation.com
Conanicut Island USA
