![Welcome to the NavList Message Boards.](../sx1.jpg)
NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Time of full moon
From: Paul Hirose
Date: 2019 Dec 13, 22:10 -0800
From: Paul Hirose
Date: 2019 Dec 13, 22:10 -0800
On 2019-12-12 12:02, Fred Hebard wrote: > The fullest of the full moon was meant to occur last night on December 12 at 12:12 am, eastern standard time. It was billed as the 12-12-12-12 moon! According to JPL Horizons the Moon phase angle reached a minimum of 1.6621° at Dec 12 05:31 UTC. That's the Sun - Moon - Earth angle. My result doesn't necessarily contradict the above time, which is possibly for an observer at the surface, not the geocenter. I haven't looked into the sensitivity of this phenomenon to the observer location (geocentric vs. topocentric). Phase angle changes slowly even at .0001° precision, so its minimum isn't as sharply defined as, for example, an equinox or solstice. As for the last two columns in the table (phase angle bisector), I confess they are beyond my comprehension. But I include the Horizons explanation. Date__(UT)__HR:MN:SC.fff S-T-O phi PAB-LON PAB-LAT 2019-Dec-12 05:28:00.000 1.6628 1.6624 79.6640 -0.8356 2019-Dec-12 05:28:30.000 1.6628 1.6623 79.6665 -0.8354 2019-Dec-12 05:29:00.000 1.6627 1.6622 79.6690 -0.8352 2019-Dec-12 05:29:30.000 1.6627 1.6622 79.6715 -0.8350 2019-Dec-12 05:30:00.000 1.6627 1.6622 79.6740 -0.8348 2019-Dec-12 05:30:30.000 1.6627 1.6621 79.6765 -0.8346 2019-Dec-12 05:31:00.000 1.6627 1.6621 79.6790 -0.8344 2019-Dec-12 05:31:30.000 1.6627 1.6621 79.6815 -0.8342 2019-Dec-12 05:32:00.000 1.6627 1.6621 79.6840 -0.8340 2019-Dec-12 05:32:30.000 1.6628 1.6622 79.6864 -0.8338 2019-Dec-12 05:33:00.000 1.6628 1.6622 79.6889 -0.8336 Column meaning: TIME Times PRIOR to 1962 are UT1, a mean-solar time closely related to the prior but now-deprecated GMT. Times AFTER 1962 are in UTC, the current civil or "wall-clock" time-scale. UTC is kept within 0.9 seconds of UT1 by introduction of integer leap-seconds for 1972 and later. S-T-O = "S-T-O" is the Sun->Target->Observer angle; the interior vertex angle at target center formed by a vector to the apparent center of the Sun at reflection time on the target and the apparent vector to the observer at print-time. Slightly different from true PHASE ANGLE (requestable separately) at the few arcsecond level in that it includes stellar aberration on the down-leg from target to observer. Units: DEGREES phi PAB-LON PAB-LAT = "phi" is the true PHASE ANGLE at the observer's location at print time. "PAB-LON" and "PAB-LAT" are the J2000 ecliptic longitude and latitude of the phase angle bisector direction; the outward directed angle bisecting the arc created by the apparent vector from Sun to target center and the astrometric vector from observer to target center. For an otherwise uniform ellipsoid, the time when its long-axis is perpendicular to the PAB direction approximately corresponds to lightcurve maximum (or maximum brightness) of the body. PAB is discussed in Harris et al., Icarus 57, 251-258 (1984). Units: DEGREES, DEGREES, DEGREES, DEGREES