Harvest moon heaven

There are so many songs, poems, and myths about the moon and moonlight. One of the best ones is the old classic, “Shine on Harvest Moon.”

If the weather cooperates this coming week the moonlight will really feel right because we’ll be approaching a full harvest moon. When darkness sets this weekend we’ll have what’s known as a waxing gibbous moon that’s basically a half moon heavily rounded off on the right. It will be perched in the southern sky. As the week goes on the moon will start out the evening more and more in the eastern sky and it will become rounder and rounder. The moon is officially full this Thursday, but by Wednesday 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 on Sept. 6.

It’s no secret that I, and most star watchers, have mixed feelings about full moons. They mostly definitely 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 on Friday, Sept. 22. 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, farmers could extend their time in the fields. Sometimes they could pull “all nighters” by the light of the silvery harvest moon. Of course it was easy to miss some spots but heck, the sleep deprived farmers and their families could mop those up the next day. Even now with headlights on tractors the full harvest moon is still a friend to farmers, or even those like me who put off cutting the lawn until evening and have to use the light of the moon with maybe the flashlight app on my phone to get the job done no matter how much I disturb my neighbors!

Honestly, 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 orange-ish 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. There’s a lot more dust and pollutants, natural and otherwise. That thicker atmosphere scatters away all but the reddish orange components of the moon’s light. When the moon climbs higher and higher, you see it through less and less atmosphere and you can see the full spectrum of its light, which melts into the familiar white that we enjoy in the crisp autumnal air. This same thing even happens to stars and planets.

Another thing you’ll notice is that the moon appears gigantic when it first rises, but shrinks after an hour or so. This is a complete optical illusion! The moon just seems bigger when it first rises because you’re comparing it with land objects — trees, buildings, strip malls, or whatever.

You can prove to yourself that the moon is no bigger when it rises. There are several ways to do this. One is with a normal run of the mill paper clip. Hold that paper clip out at arm’s length and bend it completely apart so the moon fits exactly between the two ends. About two hours later take that same bent apart paper clip and once again hold it at arm’s length toward the seemingly smaller moon. Guess what? It will fill the space between the paper clip ends exactly as it did at moonrise. The moon will not be any smaller. It will have the same diameter, I guarantee!

If you really want to take away the optical illusion of the giant moon, here’s what you do — at your own risk. Face away from the rising moon, bend forward and watch the rising moon between your legs. If you can make it that far be sure you have loose pants on or you’re going to hear a big ripping sound! If you’re still able to stand up, the full harvest moon will look a lot smaller as it does when it’s higher in the sky. Hopefully the next day you can still walk! You might want to get a local chiropractor on speed dial on your phone.

Early morning celestial hugging this week: The planets Venus and Mars are still in an extremely close celestial conjunction in the low eastern sky during early morning twilight. next Thursday and Friday morning the two planets will appear to be almost touching, less than a half a degree apart! That’s much less than the width of one of your fingers held at arm’s length. Venus is the brighter of the two and is about 145 million miles from Earth. Mars is much farther at nearly 233 million miles away. Next year, though, in late July, Mars and Earth will only be separated by just under 36 million miles, the closest Mars has been to Earth since 2003!

Mike Lynch is an amateur astronomer and professional broadcast meteorologist for WCCO Radio in Minneapolis/St. Paul and is author of the book, “Stars: a Month by Month Tour of the Constellations,” published by Adventure Publications available at bookstores at http://www.adventurepublications.net.