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Shine On, Harvest Moon


Last updated 11/9/2023 at 1:29pm

Farmers used to use the September full moon to work later into the evening.

If I were to ask you what makes the harvest moon so special, would you know the answer?

Many stargazers know that the harvest moon occurs during the autumn, around the time that harvests take place. Some might even say that it's noted for appearing very large and red when it rises. Both answers are correct to some degree, but there are some details you might not know about.

The harvest moon is so named because it's the full moon that occurs closest to the autumnal equinox (the first day of autumn). This month, the moon will achieve its "full" phase at 5:57 a.m. EDT (2:57 a.m. PDT) on Sept. 29 but will appear mostly full on the night before and after this.

Here's something you might have never noticed. The moon typically rises about 40 to 45 minutes later every evening, but during autumn it rises only half an hour or so later each night. Of course, this depends on where one lives, but in general this is true.

This was a benefit to farmers back in the days before artificial lighting and efficient machinery. They could use the September full moon's light to extend their harvesting day a bit into the early evenings for a few days or so around the equinox. They soon began to know this full moon as the harvest moon.

Many folks believe that this particular moon appears larger and redder when it rises, but if you watch the moon rise, you'll discover that this happens whenever the moon appears near the horizon.

When the moon (or the sun, for that matter) appears low in the sky, it often takes on a reddish cast. This is because the extra atmosphere through which its light must travel removes much of its shorter wavelength light, leaving it with an orange or reddish color. By the time the moon (or the sun) rises higher, its light passes through less obscuring atmosphere and its whitish color returns.

Folks tend to remember the harvest moon – perhaps because of the famous early 1900s song "Shine On, Harvest Moon" – but some may not be aware that every full moon of the year has a special name given to it by early inhabitants of North America.

For example, we know the full moon of June as the "strawberry" moon, perhaps because strawberries are in season around that time. Six months later, during the long and frigid nights of the Northern Hemisphere, we know the December full moon as the "cold" moon or the "long nights" moon.

Then, of course, there's the "supermoon." This isn't one of these historically relevant names, just a moniker that someone recently assigned to the full moon occurring around perigee – its closest point to Earth. I find this particularly silly and meaningless since there's nothing "super" about it. It's just a full moon that lies a bit closer and may appear slightly larger than normal.

OK, enough of this science and history stuff ... be sure to get outdoors this week to watch the sun set and, on the opposite side of the sky, the rising of the full harvest moon.

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