It’s hard to believe, but the old song “Shine on Harvest Moon” is well over a hundred years old. It’s an old song written by a married couple in the days of vaudeville.

I know there are many other songs involving the moon, but this one is very appropriate this week, as old and unhip as it is. If you’re under 40, you may not have ever even heard it, and in that case, check out on YouTube at http://www.youtube.com/watch?v=D7Mu9fh23dY. It’s one of my favorite versions recorded by Ruth Etting in 1931. I’m not afraid to say that’s one of my favorite lunar tunes.

This weekend we officially have a full harvest moon over Butler that will linger in the sky most of the coming week. It’s called the harvest moon because it’s the closest full moon to the date of the autumnal equinox, the first day of fall on Sept. 22, less than two weeks away.

The harvest moon really doesn’t look all that different than any other full moon. You may have seen a picture of a big orange harvest moon rising. Full moons the rest of the year appear just as large and orange. The moon sports that orange-red color when it rises or sets because when it’s close to the horizon, we see it through the thicker and dustier layers of Earth's atmosphere. That scatters away all but the reddish components of the white light of the moon.

When the moon is higher and we don’t see the moon through as much of our atmosphere, the scattering effect goes away. The reason full moons look much larger when they rise or set is simply an optical illusion. Prove that to yourself by holding a nickel out at arm's length when the full moon is rising and again when it's at its highest around midnight, and you'll see that your nickel will cover exactly the same amount of the moon.

Astronomically the harvest moon is special because of the unique celestial mechanics of this time of year.

The moon migrates eastward among the stars each night because of its 27.3 orbit around Earth. Because of that, the moon usually rises about 30 to 60 minutes later each night.

Around the time of the autumnal equinox though, the moon rises only 20 minutes later each night. The exact details of why this happens are a little too airy to explain here.

Anyway, it’s called the harvest moon because historically it helped farmers get their crops in this time of year. In the days before lights on tractors, farmers used every speck of daylight they could to bring in the crops. During harvest moon time, they got just enough extra light over a string of several nights to pull “all-nighters.”

For amateur astronomers and stargazers like myself, serious stargazing is shut down during a full moon. There’s just too much light in the sky. That’s OK though, because harvest moon time is just so magical!

Mike Lynch is an amateur astronomer and retired broadcast meteorologist for WCCO Radio in Minneapolis/St. Paul. He is the author of "Stars: a Month by Month Tour of the Constellations," published by Adventure Publications and available at bookstores and adventurepublications.net. Contact him at mikewlynch@comcast.net.