Here comes the Harvest Moon – Find out what makes it special

The Harvest Moon rises over Lake Superior in Duluth, Minn. When you’re out enjoying this year’s full moon on Wednesday and Thursday nights, watch for the dark band you see in the photo. That’s the Earth’s shadow. It’s visible for about 15-20 after sunset and topped by the pink-tinged Belt of Venus, where the atmosphere is still reflecting reddened sunlight. Credit: Bob King

Every month’s full moon tells us a little about the season. That’s why the Cold Moon happens in February and May’s moon is named for flowers. The Harvest Moon refers to the late summer-early fall harvest time, which many of us partake of in a small way with our gardens. My tomato harvest just wrapped up, but there’s still a zucchini or two on the way.

You’ve probably noticed how squished the moon looks when it first comes up. Stronger refraction from the thicker, denser air closer to the horizon “lifts” or refracts the bottom part of the moon upward more than the top, “squeezing” it into an egg shape. Once the moon’s higher up, air density is more uniform, refraction effects less and the moon looks round. Credit: Bob King

The Harvest Moon is the full moon that occurs closest to the autumnal equinox, the first day of fall in the northern hemisphere. This year that happens overnight on Sept. 18-19. Since full moon dates bounce around a bit, the Harvest Moon can happen anywhere from mid-September to mid-October, making it the only full moon to carry the same name in two different months.

The Harvest Moon harks back to our agrarian past when farmers used its welcome light to continue harvesting their crops past sundown. WIth electricity, moonlight was important part of farming. Once the crop was ripe, you needed to gather it up as soon as possible, and that could mean working into the night.

The travels east (to the left seen in the northern hemisphere) as it orbits Earth at the rate of one moon diameter an hour. Illustration: Bob King

It’s the Harvest Moon’s angle to the horizon that makes it unique and useful. Because the angle of the full moon’s path to the horizon is very shallow in September and October, the time difference between successive moonrises is only about 20-30 minutes instead of the usual 50-60. With moonrise happening on the heels of sunset, the Harvest Moon’s return at practically the same hour gave farmers nearly continuous light from sunset to sunrise to work the crops.

Night to night the moon moves about 12 degrees along its orbit or a little more than one fist held at arm’s length to the east. You can see this for yourself by referencing the moon’s location with respect to a bright star in its neighborhood.

The angle of the moon’s path to the horizon makes all the difference in moonrise times. At full phase in September, the moon’s path is nearly parallel to the horizon with successive moonrise just 25-30 minutes apart. In spring it tilts steeply southward, delaying successive moonrises by over an hour. Moonrise times are shown for the Duluth, Minn. region. Illustration: Bob King

Around the time of September’s full moon, a significant amount of that 12 degrees is toward the north direction which causes the moon’s path at the horizon to flatten out. A shallow path means the moon’s eastern movement only puts it a little bit further below the horizon for several nights around full moon. Earth only has to rotate for 20 to 30 minutes to carry the moon into view. Six months ago at the spring equinox, the full moon’s path was much more steeply tilted to the horizon and night to night rising times more than an hour apart.

A Harvest Moon rises over a desert landscape near Bishop, Calif. Credit: Andrew Kirk

That’s why I call spring the time-when-the-moon-gets-out-of-the-sky-in-a-hurry as opposed to the current full moon that never sleeps. While I’ve been known to gather my garden goodies by moonlight when frost threatens, most of us can take advantage of the full moon’s slanted path to enjoy night after night of watching a big moon rise without to stay up late. Consider it a harvest of moonlight and a veritable feast for the eyes.

Since full moon occurs during the early morning hours of the 19th across the Americas, the moon will look almost identically full on both Sept. 18 and 19. Two nights of the Harvest Moon – can it get any better? Click HERE to find out when the moon rises for your town. If you take a photo, please send me a copy at rking@duluthnews.com. I’ll publish a little gallery on the 20th. Thanks!

8 thoughts on “Here comes the Harvest Moon – Find out what makes it special

  1. Bob, thanks again for your terrific blog. What’s the very bright object to the “left” of Orion in the morning sky. It’s much brighter than Sirius.

  2. Shine on Harvest Moon, my favorite Full Moon takes place on our 26th Wedding Anniversary this year as the Moon seems to face Venus and Saturn in the evening west.

  3. I am not much into day time Astronomy but since Venus can be seen with the naked eye before sunset and easy in binoculars, is it likely using Venus as a guide that I could see Saturn in 20 x 60 binoculars, say 40 minutes before sunset? Practice, Viewing these objects during daylight might make viewing Comet ISON a little easier in daylight with binoculars say 3-5 days before perihelion or before it gets real close to the Sun.

    • Edward,
      You might be able to. Sounds like an interesting experiment. I should think that a tripod (or other stable platform)for the binoculars would be essential. Go for it and let us know.

  4. Bob, I thought that this was interesting. I went on the site Comets this week. And from what I have seen reported up till now if all goes as would be average. I deduced to the best of my knowledge that Comet ISON should be brighter than magnitude 9 from around October 23 through January 25, 2014. Then looking at Comet Lovejoy, I came up with the dates of October 23 through January 28. I did not use pinpoint accuracy but it looks like these comets may be somewhat identical except when ISON is close to the Sun it should make for a much brighter show. But these dates I have used may be changed in a week or 2. It is now starting to get exciting as we get close to knowing what will actually happen.

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