Last Saturday was the Autumnal Equinox here in the northern hemisphere, which makes this coming Saturday's (Sept. 29) full moon the "Harvest Moon."
What does that mean, and how is this event special for Alaskans? First, it helps to think like an Outsider.
Down in the Lower 48, the Full Moon that occurs nearest the Autumnal Equinox is considered to be a pretty special sight. That's because at this time of year, the Moon's orbital path around the Earth makes a particularly shallow angle with the eastern horizon at sunset. So at this time of year, the Moon's own orbital motion is moving its sunset position mostly northward (around the horizon), rather than mostly eastward (below the horizon).
The upshot of all this is, at this particular time of year, moonrise happens only 30 minutes or so later every night (compared to nearly 53 minutes later for the Full Moon in March). And if you've ever tried to figure out exactly when the Moon is completely full, you'll have noticed that it looks very nearly full for a few days before and after the official Full Moon.
So the "Harvest Moon" is a time when the nearly-full Moon rises at "about" the same time every night for 3-5 nights in a row, before the Sun's light has faded from the sky. This was seen as a benefit to farmers back in the days before artificial lighting, because they could continue harvesting their crops by the light of the Moon.
Now, for Alaska, something special!
Silly Outsiders! They think that 30 minutes is a big deal.
Well up here in Anchorage, our Harvest Moons rise only 10-15 minutes later every night for 5 nights in a row!
That's because we're about 20 degrees further north than your average Lower 48er, which means our skies are rotated southward by about 20 degrees from theirs. (See the Starry Night screenshots at the end of this story.)
At this time of year in Anchorage, the Moon's orbit is carrying it nearly parallel with the eastern horizon at sunset. And if you live even further North that alignment gets even better.
Two hundred miles north of Fairbanks, just north of the Arctic Circle, the fullish moon rises at the same minute on the clock for 5 days in a row.
Public Events at UAA Oct. 1-5
Oct. 1 5-7 pm 'Developments in the Arctic: How best to proceed'
Parking is always free at UAA Campus Bookstore events.
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