Posted on by Bob King

Rare ‘Harvest Supermoon’ Makes for a Super Eclipse September 27

Get set for a superlative eclipse. On Sunday night, September 27 in the Americas (early Monday morning for Europe and Africa) the Full Moon will slide into Earth’s shadow in total eclipse. This is no ordinary Full Moon. It’s the Harvest Moon, the full Moon that occurs closest to the autumnal equinox.

It also happens to reach perigee — its closest point to the Earth — on the very same night, making this a supermoon eclipse. Oh, and this is no ordinary perigee. It so happens to be the closest Full Moon of 2015! Supermoon eclipses are rare; the last one occurred in 1982 and the next won’t happen till 2033.

The supermoon of March 19, 2011 (right), compared to an average moon of December 20, 2010 (left). Note the size difference. Image Credit: Marco Langbroek, the Netherlands, via Wikimedia Commons.
The supermoon of March 19, 2011 (right), compared to an average moon of December 20, 2010 (left). Note the size difference. Credit: Marco Langbroek, the Netherlands, via Wikimedia Commons.

The average Earth-Moon distance is 240,000 miles (386,000 km), but on Sunday night our red-faced companion will edge within 221,752 miles (356,876 km) of Earth and appear 8% larger than normal. Will you be able to see the difference?

Observers in the eastern half of the U.S. can watch the entire eclipse, while those living in the far western states will see the Moon rise already in partial eclipse. If you’re reading this from Europe or Africa, you’ll have to get up early because partial phases start just after 2 a.m. Universal Time Monday morning September 28.

A total lunar eclipse occurs during a Full Moon when the Sun, Earth and Moon line up precisely in that order. Light from the Sun (white lines) skirts the Earth's atmosphere, which bends and reddens it. It reaches and reflects off the Moon back toward the Earth and we see a beautifully colored disk during totality. Credit: NASA with additions by the author
A total lunar eclipse occurs during a Full Moon when the Sun, Earth and Moon line up exactly in that order. Light from the Sun (white lines) skirts the Earth’s atmosphere, which bends and reddens it. It reaches and reflects off the Moon back toward the Earth and we see a beautifully colored disk during totality. Credit: NASA with additions by the author

Lunar eclipses occur on average 2-3 times a year and are visible wherever the Moon is up or about half the globe. Were it not for the Moon’s orbit being tilted 5.1° relative to Earth’s orbit, we’d see a total eclipse every Full Moon. The tilt means the Moon normally misses Earth’s shadow at Full Moon, passing a few degrees north of south of the cone.

Six months after the of 1982 July 06 eclipse, a second total eclipse was visible from the USA on 1982 Dec 30. But this time, the totally eclipsed Moon almost vanished completely from sight. Dust from the recently erupting Mexican volcano El Chichon was still suspended high in Earth's atmosphere where it blocks most of the Sun's rays from reaching the Moon.
The totally eclipsed Moon of December 30, 1982 almost vanished completely from sight. Dust from the then-erupting Mexican volcano El Chichon was still suspended high in Earth’s atmosphere where it blocked most of the Sun’s rays from reaching the Moon. Credit and copyright: Fred Espenak

Not this month. On Sunday night, the Moon will pass squarely around the backside of the planet and enter Earth’s inner shadow called the umbra. In the umbra, the only sunlight that reaches the Moon is the bit that’s refracted and reddened by our atmosphere. It spills into the darkness to tint the Moon an amazing array of colors ranging from yellow to dingy brown-black. The colors vary with the state of the atmosphere.

Diagram showing the Moon's progress during the upcoming eclipse. Both CDT and UT times are given. Credit: NASA / F. Espenak
Diagram showing the different phases of the upcoming eclipse. Both CDT and UT times are given. The Moon first travels through the outer partial shadow called the penumbra before reaching the umbra. Credit: NASA / F. Espenak

When levels of aerosols like desert and volcanic dust are low, the eclipsed Moon shines brightly in yellows and oranges. When high, especially in the wake of a major volcanic eruption, the atmosphere can be so choked with dust and other aerosols that the Moon nearly disappears from view. Part of the fun of eclipse-watching is not knowing quite what to expect until the Moon finally slips into the umbra.

View facing southeast at the start of totality around 9:15 p.m. CDT as seen from Minneapolis, Minn. The Moon will be in Pisces not far from the asterism dubbed "the Circlet". Source: Stellarium
View facing southeast at the start of totality around 9:15 p.m. CDT as seen from Minneapolis, Minn. The Moon will be in Pisces not far from the asterism dubbed “the Circlet”. Source: Stellarium

En route to the umbra, the Moon first passes through the penumbra or outer shadow. This region of partial shadow —  a mix of shadow and sunlight poking over the top or bottom of the Earth — shades the Moon but weakly. That’s why entry into the penumbra isn’t noticeable visually. But about 20 minutes before the partial phases begin, you’ll notice that the leading edge of the Moon (east or left side) looked dusky and blunted. It’s a cool view, so be sure to watch for it.

Animation of the Sept. 27-28 eclipse showing the Moon passing through Earth's shadow. Credit: Tom Ruen
Animation of the Sept. 27-28 eclipse showing the Moon passing through Earth’s shadow. Credit: Tom Ruen

Total lunar eclipses make for leisurely affairs. This one lasts more than 3 hours with 1 hour 12 minutes of totality; it all happens during convenient twilight and early evening viewing hours for most observers in the Americas and Canada. If you’ve felt a certain rhythm to eclipses in the past year and a half, you’re in touch with the cosmic vibe. September’s eclipse will be the fourth and final of the famed “bloody tetrad” of eclipses spaced six months apart that began back in 2014.

September 27-28, 2015 eclipse visibility map. Credit: NASA / Fred Espenak
September 27-28, 2015 eclipse visibility map. Credit: NASA / Fred Espenak

Make sure you catch this one. Skywatchers in the Americas won’t see another lunar totality until January 31, 2018. One of my favorite things to watch during eclipses is the return to darkness during totality. You look up and see all the stars the Moon stole away just an hour ago, and there in the middle of it hangs this ruddy orb that looks more like an alien planet than our familiar satellite.

Below I’ve listed times for each U.S. time zone for the different phases of the eclipse. If you’re interested in photographing the Moon, check out my photo primer for helpful tips. And don’t forget to take the kids out for a look. Lunar eclipses are perfectly safe to view, and this one’s early enough for many children to see. Clear skies! (But if it’s cloudy at your house, you can watch the eclipse live here or here.)

Eclipse Events EDT CDT MDT PDT
Penumbra first visible 8:45 p.m. 7:45 p.m. 6:45 p.m. 5:45 p.m.
Partial eclipse begins 9:07 p.m. 8:07 p.m. 7:07 p.m. 6:07 p.m.
Total eclipse begins 10:11 p.m. 9:11 p.m. 8:11 p.m. 7:11 p.m.
Mid-eclipse 10:48 p.m. 9:48 p.m. 8:48 p.m. 7:48 p.m.
Total eclipse ends 11:23 p.m. 10:23 p.m. 9:23 p.m. 8:23 p.m.
Partial eclipse ends 12:27 a.m. 11:27 p.m. 10:27 p.m. 9:27 p.m.
Penumbra last visible 12:45 a.m. 11:45 p.m. 10:45 p.m. 9:45 p.m.