Total Eclipse of the Harvest Moon
In the days before light bulbs, farmers relied on moonlight to help them harvest their crops. Many crops ripen all at once in late summer and early autumn so farmers found themselves extremely busy at this time of year. They had to work after sundown. Moonlight became an essential part of farming, and thus, the Harvest Moon was born.
According to folklore, the Harvest Moon is the full Moon that falls closest to the autumnal equinox, the hectic beginning of northern autumn. In 2015, the Moon is full on Sept. 28th, less than a week after the equinox of Sept. 23rd. The coincidence sets the stage for a nice display of harvest moonlight.
But wait. This year’s Harvest Moon is not like the others. It’s going to be eclipsed.
On the night of Sept. 27 and into the early hours of Sept. 28, the full Moon will glide through the shadow of Earth, turning the Harvest Moon a golden-red color akin to autumn leaves.
The action begins at 9:07 PM Eastern Time on the evening of Sept 27th when the edge of the Moon first enters the amber core of Earth’s shadow. For the next three hours and 18 minutes, Earth's shadow will move across the lunar disk.
Totality begins at 10:11 PM Eastern Time. That’s when the Moon is completely enveloped by the shadow of our planet. Totality lasts for an hour and 12 minutes so there is plenty of time to soak up the suddenly-red moonlight.
The reason the Moon turns red may be found on the surface of the Moon itself. Using your imagination, fly to the Moon and stand inside a dusty lunar crater. Look up. Overhead hangs Earth, nightside facing you, completely hiding the sun behind it. The eclipse is underway.
You might suppose that the Earth overhead would be completely dark. After all, you’re looking at the nightside of our planet. Instead, something amazing happens. When the sun is located directly behind Earth, the rim of the planet seems to catch fire! The darkened terrestrial disk is ringed by every sunrise and every sunset in the world, all at once. This light filters into the heart of Earth's shadow, suffusing it with a coppery glow.
Back on Earth, the shadowed Moon becomes a great red orb.
One more thing: The full Moon of Sept. 28th occurs near the perigee of the Moon’s orbit—that is, the point closest to Earth. This makes the Harvest Moon a “supermoon.”
The super Harvest Moon eclipse will be visible from the Americas, Europe, and Africa. It brings an end to a remarkable series of four consecutive total lunar eclipses visible from North America—a so-called “tetrad.” Perhaps the heavens have saved the best for last.
If you live in the eclipse zone, mark your calendar for Sept. 27-28, and enjoy the show.
For more beautiful sights in the night sky, stay tuned to science.nasa.gov