Characteristics of the Harvest Moon

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Everyone appreciates the breath taking size and color of the Harvest Moon. But how did it get its name? When does it rise, and, why the spectacular color?

The Harvest moon occurs when the moon is at, or closest to, its fullest circumference near the autumn equinox. When the moon is in one direction and, the sun us in the other, the sun fully illuminates the moon. Night and day are of equal length at this time.  It is not to be confused with the Hunter’s moon which is actually the first full moon after the Harvest moon.

The Harvest moon was considered especially helpful in the past because of the short period of time between sunset and its rising.  This enabled farmers to work later in their fields during the harvest due to the extra light provided by the moon, giving the moon its name. The reason for this short time between sunset and moon rise is that the plane of the Earth’s orbit around the sun makes a narrower angle in relation to the horizon in the evening in autumn.

It can occur either before or after the autumn equinox and if it occurs on the same night as the equinox it is called the Super Harvest Moon.

The reason for its bright fiery coloring has to do with the Earth’s atmosphere. When the moon is full in the sky it completely reflects the sun’s white light, without atmospheric disturbance. The Harvest Moon, however, enjoys its red glow because as it slowly rises after sunset the full brunt of the atmosphere on the horizon absorbs the blue light from the sun and transmits the red light.   

Its size difference is actually a trick of the eye that occurs with any full moon and is referred to as the moon illusion. Any celestial body seen low in the sky appears to be larger than it actually is. Want to check? Stand with your back to the moon and then look back at it through your legs. This gives you proper perspective and it no longer seems so large.

This year was the first Super Harvest Moon since 1991. NASA described it as a “‘360-degree, summer-autumn twilight glow’ that hasn’t been seen in nearly 20 years.”  The next time we’ll be able to see this phenomenon is in 2029 according to a NASA science news webpage.

Every autumn we get to enjoy this beautiful, colorful feature in our night sky.  Take time to enjoy it. It’s an inspiring sight.

More about this author: Beth Janvrin

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