If it feels like a while since the Moon took a deep dive into Earth’s shadow, you’re right. The last total lunar eclipse occurred on January 21, 2019, followed by four penumbral eclipses in 2020. Wait no more! On May 26th, observers in the western half of North America, western South America, East Asia, and Australia will once again see the Moon fully eclipsed.
This eclipse will be short and sweet much like the total solar variety, with the Moon spending just 15.9 minutes inside the umbra, Earth’s central shadow. The brief visit is due to two factors. First, the Moon passes well north of the umbra’s center with its northern limb nearly tangent to the umbra’s edge. Minutes after it enters the shadow, it pushes out the other side.
Secondly, the eclipse happens to coincide with a perigean full Moon (known popularly as a supermoon). In fact, May’s Flower Moon is the closest full Moon of the year. Perigee, the point in its orbit of closest approach to the Earth, occurs on May 25th at 9:53 p.m. EDT, only about 9.3 hours before mid-eclipse. Distance from the Earth affects both the Moon’s apparent size and velocity. The full Moon’s average apparent diameter is 31′, but during May’s totality it will be 33.6′ across, a difference of about 8%. This extra-large Moon makes for a slightly tighter fit within the umbra, leading to a quicker egress.
The Moon will also be traveling faster along its orbit. On May 11th when it was at apogee, its most distant point from the Earth, it clocked in at 3,528 kilometers per hour (2,192 mph). During totality on the 26th, our satellite will be sailing along almost 250 kilometers an hour (155 mph) faster. The extra speed hastens its exit from the shadow.
While totality is restricted to the regions described earlier, half the planet will witness a partial lunar eclipse, from eastern South America to India. Across the U.S. and Canada, the farther west you live, the deeper the Moon appears in eclipse.
From the Eastern seaboard only the early penumbral phase will be visible before the Moon sets around sunrise. From the Midwest about half the Moon will be covered, while from Denver westward, observers will enjoy a total eclipse. Only in the far western states will totality be visible in a dark sky, otherwise this is a morning twilight event. Because the Moon lies in Scorpius well south of the ecliptic, it will shine low in the southwestern sky across much of the U.S. and Canada, so be sure to scout out a location with an unobstructed view in that direction.
At the start of the eclipse, the Moon enters the Earth’s outer shadow, called the penumbra. Here the planet’s globe only partially blocks the light of the Sun, diluting the shadow and making it a challenge to see. But if you pay close attention, you’ll notice a gray shading across the eastern third of the Moon about 20 minutes before the Moon enters the dark, inner umbra, marking the start of the partial eclipse.
|Penumbral eclipse begins||4:47 a.m.||3:47 a.m.||2:47 a.m.||1:47 a.m.||12:47 a.m.||10:47 p.m. (May 25)|
|Partial eclipse begins||5:45 a.m.||4:45 a.m.||3:45 a.m.||2:45 a.m.||1:45 a.m.||11:45 p.m.
|Totality begins||_____||_____||5:11 a.m||4:11 a.m.||3:11 a.m.||1:11 a.m.|
|Maximum eclipse||_____||_____||5:19 a.m.||4:19 a.m.||3:19 a.m.||1:19 a.m.|
|Totality ends||_____||_____||5:27 a.m.||4:27 a.m.||3:27 a.m.||1:27 a.m.|
|Partial eclipse ends||_____||_____||_____||5:53 a.m.||4:53 a.m.||2:53 a.m.|
|Penumbral eclipse ends||_____||_____||_____||_____||_____||3:50 a.m|
Partial eclipse begins when the umbra takes that first nibble from the lunar limb. Not long after, when roughly a quarter of the Moon has entered the inner shadow, its reddish hue becomes noticeable without optical aid. The color comes by way of our atmosphere, which refracts reddened sunlight grazing the planet’s circumference into the depths of the umbra. Sans atmosphere, the Moon would be completely invisible during totality.
The Moon’s color in the shadow ranges from a bright copper to a deep maroon-brown, influenced by how centrally it passes through the umbra as well as the amount of suspended aerosols in the Earth’s atmosphere at the time of eclipse. The more material, the more light absorbed and the darker the Moon.
I suspect May’s totality will be a bright one if only because the Moon barely scrapes through the umbra. During its brief foray, watch for ozone in the upper stratosphere to work its magic. Ozone absorbs red light and colors the outermost fuzzy fringe of the umbra blue, a sight best seen in binoculars or a telescope.
During any phase of the eclipse — but especially during totality — watch for potential meteoroid impacts. They’ll appear as momentary flashes of light on the darkened moonscape. Amateurs captured one of the best-known impact flashes on video during the 2019 eclipse. If you have a second telescope and video capability, consider dedicating that instrument to impact recording. For still photography tips I recommend Fred Espenak’s How to Photograph a Lunar Eclipse.
If you’re lucky enough to see totality from the countryside, you’ll experience the full eclipse aesthetic as the sky transitions from bright moonlight to black velvet. With the Moon in shadow, thousands of stars return to view along with the grand arch of the summertime Milky Way. Maybe it’s just synesthesia, but when moonlight is quenched at totality, a hush seems to settle over the land.
During the eclipse, the Moon will appear very close to a pair of 4th-magnitude stars, Omega1 and Omega2 (ω1, ω2) Scorpii, and about 1° southeast of the beautiful double star Beta (β) Scorpii. Antares lies about 6.5° southeast. One or both of the Omegas will be occulted around eclipse time from Mexico, Central America, and parts of South America. Beta will be occulted prior to the eclipse from southern South America.
Whatever percentage of the Moon is covered, I wish you clear skies. Don’t forget. You’re part of this celestial alignment, too!
If you’re interested in reading more about this and other celestial events this month click here to purchase a copy of the May issue of Sky & Telescope.