The full Flower Moon ducks inside Earth’s shadow in a total lunar eclipse this month. Prepare for all the highlights of the special event.
You can't do better for an astronomical event than a total lunar eclipse. It's visible to city and rural residents alike across half the planet, requires no special equipment, lasts for hours and is guaranteed to happen. How many other celestial shows offer this kind of ease and certainty? About the only thing that can get in the way are clouds. And for that, you can check current cloud maps to find the nearest clear skies. More about that in a moment.
On Sunday night–Monday morning May 15–16, the Moon will undergo a total eclipse widely visible across the Americas, Europe, and Africa. From the East Coast partial eclipse begins about two hours after sunset, an hour after sunset for the Midwest, and near sunset for the mountain states.
Farther west along the West Coast, the moon will rise fully immersed in Earth's shadow. While that may make it sketchy to see at first, as the sky darkens, dramatic views of a highly reddened Moon near the horizon will make for stirring photographic possibilities. In the Eastern Hemisphere, European and African observers will witness the eclipse in the early morning hours and at dawn.
A nod to nodes
Total eclipses would occur at every full Moon if the Moon's orbit were coplanar with the Earth's, but it's inclined by 5.1°. The two orbits intersect at two places called nodes. If the Moon happens to be full at the same time that it crosses at or near a node, it will pass directly into Earth's shadow, and we'll see an eclipse. That typically happens twice a year with a maximum of three and minimum of zero. Happily, 2022 is one of those "typical" years, with a second total eclipse falling on November 7–8 and also visible in the Americas.
If you can only afford a half-hour, watch the transition from partial to total (or total to partial if you live in the far west) eclipse. But if you're able, try to observe as much of the event as possible, so you can experience the majesty of the event at nature's pace. The primary eclipse lasts nearly 3½ hours, with an additional ~20 minutes of penumbral shading visible on either side.
Let's check out the highlights.
|Penumbra first visible?
|Partial eclipse begins
|Total eclipse begins
|Total eclipse ends
|Partial eclipse end
|Penumbra last visible?
Penumbral eclipse — Look for a subtle shading along the eastern third-to-half (bottom left for U.S. observers) of the Moon. When will it first become visible — 30 minutes before partial eclipse? 15 minutes? Can you detect color and depth of shading or is it a uniform gray?
Partial eclipse — At what point does the shadowed portion of the Moon appear red in binoculars? With the naked eye? Because it absorbs red light, the atmospheric ozone layer often imparts a turquoise hue to the edge of encroaching umbral shadow. You'll need a small telescope to see the coloration, but it's surprisingly obvious once you look for it.
Telescope users can also time when the shadow's edge passes over individual craters to help determine how changes in the Earth's atmosphere cause the expected diameter of the umbra to vary. For predictions and a chance to share your observations, visit Roger Sinnott's Useful Projects for a Lunar Eclipse.
Totality — Since the Moon crosses the southern half of the shadow's core and not dead-center, you should see a noticeable difference in brightness and color between its southern hemisphere, located near the umbra's periphery, and the northern hemisphere, which almost touches the center. These contrasts will work together to enhance the Moon's three-dimensional appearance as a smoldering orb floating among the stars.
A dark eclipse?
The clarity of the atmosphere also affects the Moon's brightness and color during totality. Eclipsed moons can range from yellow-orange to rusty red or even brownish-gray. Dark eclipses are often tied to dust and other particulates released from volcanic activity. The powerful Tonga submarine volcano eruption that began last December and climaxed in January released a massive amount of aerosols into the upper atmosphere which still linger four months later.
Helio Vital, with the Brazil lunar-eclipse watchers, predicts that the "additional absorption layer will darken the Moon at totality by 1.5 magnitude, rendering it a very dark eclipse with a total magnitude of +0.9 (+/– 0.9 mag.)." The same eclipse viewed through a "clean atmosphere" would otherwise shine at magnitude –0.6 (+/– 0.6 mag.) at mid-eclipse. Vital writes:
"Then the totally eclipsed Moon, some 0.3 million times dimmer than the usual full Moon, will be rivalling Antares in brightness, and most eclipse gazers will be amazed to see it so faint and colorless, estimating it at L=1 on the Danjon scale." As the volcanic material spreads more evenly and completely around the globe, Vital forecasts even darker eclipses next year.
How deeply will the Moon be affected by the eruption? Use the Danjon scale chart to make your own estimate and drop us a line in the comments section. And while you're at it, also keep an eye out for any potential impacting meteoroids during totality. A strike will appear as brief, pinpoint flash against the darkened Moon.
For observers across much of the U.S., Canada, and parts of Mexico and South America the Moon occults the 6th-magnitude double star S672 around 3:45-4 UT, May 16. From the southwestern U.S. eclipse-watchers instead will see an occultation of 5.5-magnitude HD 138413. From Tucson, Arizona, the totally eclipsed Moon covers the star from 8:30 p.m. to 9:09 p.m. MST.
While the transition from daylight to semidarkness happens rapidly during a total solar eclipse, the lunar version is more casual, though not without the power to touch our emotions. As totality approaches, the sky darkens by degrees until all the stars return. Drained of direct sunlight the Moon loses its thrall over the heavens. I don't know how, but the loss of moonlight makes it feel quieter outside. Hushed. Observers under rural skies get to witness the dramatic return of the Milky Way.
Besides totality itself, my favorite phases are the twin 5-minute intervals immediately before and after, when a narrow sliver of uneclipsed Moon stands in vivid contrast to the dark, umbra-soaked globe.
As the Moon exits the Earth's shadow, you can continue to observe each phase but in reverse. Many of us will be photographing the eclipse. I recommend Fred Espenak's guide How to Photograph a Lunar Eclipse for tips. At the top I mentioned clouds. Should they threaten, here are some resources to help you find the nearest clear sky:
Weather Network interactive satellite cloud viewer
U.S. 7-Day Cloud Cover Forecast
GOES-East and GOES-West live satellite images
Astrospheric smoke forecasts (from smoke from New Mexico wildfires, which could affect both the Moon's color and visibility)
If there's no escape, Italian astronomer Gianluca Masi will live-stream the eclipse on his Virtual Telescope site on May 16th starting at 2:15 UT (10:15 p.m. EDT on May 15th). You'll find additional streaming options at Griffith Observatory and timeanddate. Wishing you a wonderful night out. And if you have kids, let 'em stay up late!
Read more on the May 15–16 lunar eclipse in the May issue of Sky & Telescope.