post-full moon setting

Event Date: September 30th
Time: 7:04 AM


Brief

   While I have spent the last two entries showing the short intervals between Moon rises in the east, this next entry shows the following morning after the Moon's crest of fullness.  While (near-)full Moon rises at this time of year are on average 25-30 minutes apart, the time of them setting can sometimes be be well over an hour.  As I show the Moon below at the time of Sunrise, it is still at a good viewing altitude.  Since it continues to move north in declination for the next few days, it means that it is taking longer to set.  Also, remember that the Moon is moving east by about one diameter each hour, which also helps keep it above the horizon a little longer.

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

Detailed

   The time between sets for the Moon this morning and yesterday's is almost exactly one hour.  If the Moon wasn't approaching descending node and instead, closer to ascending node, it would mean a setting difference of perhaps a few more minutes.  Remember also, that there are times because of the precession of the nodes and declination change, the Moon rarely changes in declination at all.  The celestial guidelines above show that the Moon is moving further north of the celestial equator, while its orbit is bringing it back towards the ecliptic slowly.  Look further east (near center), and notice that descending node is still only a few days away.  When the Moon starts to move south of the ecliptic near the time of last quarter phase, while also moving to a part of the sky where the Sun is in mid-late summer, the declination change will be minimal.