By Mike Lynch
We’ll be approaching a full harvest moon this week. Saturday night was what’s known as a first quarter moon half moon perched in the southern sky.
The moon is officially full next Sunday, but by Friday it will be close enough to a full moon for most folks.
The harvest moon is a little late this year because we had our last full moon, which was a blue moon or second full moon in a month, on Aug. 31.
Most star watchers have mixed feelings about full moons. They whitewash out a lot of celestial treasures available through your telescope, but you have to be completely without feeling and emotion not to be drawn to that heavenly light. That’s especially true with the harvest moon.
Technically, the harvest moon is the full moon closest to the first day of astronomical autumn, otherwise known as the autumnal equinox, which was Saturday.
What makes the full harvest moon so special is that because of the unique celestial mechanics this time of year, the moon rises only about 20 minutes later each evening, getting the moon up in the eastern sky close to sunset for almost a week. Normally the full moon rises from 35 to nearly 60 minutes later each night so most folks, especially those with early bedtimes, don’t enjoy as many consecutive evenings of full or near full moonlight.
The harvest moon got its name because of all the help it gave farmers in the days before electricity and headlights on tractors. Since the moonlight was available in the east so close to sunset night after night they could extend their time in the fields. Sometimes they could pull all-nighters by the light of the silvery harvest moon.
The harvest moon doesn’t look all that different than any other full moon except that it seems that it has a brighter orange color for more of an extended time as it rises. The moon usually sports an orangish hue when it rises, but the rising harvest moon hangs on to its color longer into the evening.
That’s because the harvest moon rises at a lower angle with respect to the horizon, so the moon hangs lower in the sky longer. Whenever you view any astronomical object close to the horizon, you’re looking through a lot more of Earth’s atmosphere, with more dust and pollutants, natural and otherwise.
The moon seems bigger when it first rises because you’re comparing it with land objects — trees, buildings, strip malls, or whatever.
If you really want to take away the optical illusion of the giant moon, and if you dare, face away from the rising moon, bend forward and watch the rising moon between your legs. The full harvest moon will look a lot smaller as it does when it’s higher in the sky.
Mike Lynch is an astronomer and professional broadcast meteorologist for WCCO Radio in Minneapolis and is author of the book, “Washington Starwatch,” available at bookstores. Check his website, www.lynchandthestars.com.
The Everett Astronomical Society: www.everettastro.org/.