NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: North from Moon
From: Ken Muldrew
Date: 2022 Feb 20, 11:53 -0700
From: Ken Muldrew
Date: 2022 Feb 20, 11:53 -0700
A bit simpler method for getting local time from the moon at night:
1. The full moon is analogous to using the sun (divide the sky into 12, -6 hours is directly East, 0 hours is on the meridian, +6 hours is directly West; add the hour angle to noon) except we use midnight rather than noon.
2. When not a full moon, divide the moon into 12 parts and take the dark portion (e.g. a half moon has 6/12ths in darkness, so we take 6; a 1/4 moon has 8/12ths in darkness so we take 8, etc.)
3. For the Northern hemisphere, we use the mnemonic of a “C” shaped moon indicating ‘C’oncatenate (or add), and a “D” shaped moon indicating ‘D’educt (or subtract).
4. Add or subtract the dark portion of the moon to the hour angle and get local time. (e.g. tonight you might see a “C” moon at about 30 degrees East of South (or 2 hours before the meridian) with about 4/12 of the moon in darkness, so: -2 for the hour angle, +4 for the moon’s illumination - midnight - 2 + 4 = 2:00 AM).
Ken Muldrew.
On Feb 19, 2022, at 8:45 AM, Alexander Duytschaever <NoReply_Duytschaever@fer3.com> wrote:If one can see the Moon, then one can point out the Sun (usually somewhere below the horizon) by close observation of the terminator, after which one can point the hour hand of the clock to that (invisible) Sun and find the north/south axis the same way one does when using the Sun/clock method during the day.
This approach demands some "3D" insights to more or less find out the Sun direction. It will break down when approaching the equator, but the Sun/clock method will also break down there.
rgds,
-alex-
ps - the 5 degree tilt of the lunar orbit wrt ecliptic slightly adds to the problem of using the horns of the moon only.
