Moon's orbit, and more "node talk"

Event Date: January 25th

Time: 5:30 PM

Brief

  The Moon reaches crest of fullness more than 27 hours after the time above, yet it still looks nearly full when rising in the east-northeast this evening.  Although it is rising at about the same longitude as our Sun during mid-July, the Moon is not as far north as our star this time.  Precession of the nodes has brought it south of the ecliptic by more than 4º and therefore, it is only about as far north as the Sun during the first week or two of August.

   Taking a look below, I included the ecliptic and Moon's orbit, showing it being south of our Sun's path.

click on images to enlarge: courtesy of Starry Night Pro Plus, version 6.4.3, by Simulation Curriculum Corp.

Detailed

   I bent the sky slightly in the image, to show in the upper right, the descending node arrow.  This node, along with the ascending one 180º away in Sagittarius, move a full cycle around the ecliptic about every 18.6 years.  This equals 19.35º a year, and 1.61º per month, on average.  I put these numbers out there, to demonstrate how slow the process is.  The monthly movement is only that of 3 full Moons from us.  However we compare them, they are on the move regularly, hence the word "precession".  About 6 and 7 years ago, the ascending node was near the position in the sky that the Sun is for the March equinox, and the descending where the Sun is for the September equinox.  As a result, when the Moon reached full near the spot where the Sun was at the June solstice, it was about 5º further north, and about as north as it could be anywhere in the sky.  Whereas the Sun only reaches 23.5º N (rounded) in declination, the Moon was nearly 29º, and seen very close to zenith at transit in the most southern portions of the US and northern Mexico, among other locations at 29º latitude.