Behold! As the Ides of March approaches, witness as Earth’s shadow engulfs the moon!
Or, put another way, a total lunar eclipse is set to occur on the night of March 13 and into the early-morning hours of March 14. This is one of my favorite astronomical events; unlike its fast-paced and potentially hazardous solar counterpart, a lunar eclipse is slow and majestic, happens at night and doesn’t require any special equipment or optical aid to see. This makes it easy and fun to watch; you can pop outside every 15 minutes or so to check its progress, and you usually won’t miss anything.
The entire eclipse will be visible across essentially all of North America and most of South America.
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The timings of the eclipse’s various stages are given below, but to understand those, you first need to understand how all this unfolds.
The moon orbits Earth once every 27 days or so. The phase we see it in (crescent, half full, and so on) depends on the angle between the sun, the moon and Earth. When the moon is new, between Earth and the sun, we are gazing at its unilluminated half, so it looks black. When it’s opposite the sun in the sky, we see its fully illuminated half, so it appears full. The other phases occur in between these two geometries, so we see various amounts of the moon’s surface lit. Despite a common misconception, Earth’s shadow has nothing to do with the phases.
But it’s why we have eclipses! Earth’s shadow falls in the direction away from the sun, so the moon has to be opposite the sun in our sky during an eclipse. This means a lunar eclipse can only happen at full moon. As the moon orbits Earth, it moves into Earth’s shadow, creating the stages of the eclipse.
The easiest way to understand how the eclipse works is to imagine it first as if you’re on the moon, looking up at Earth and the sun. From this viewpoint—which, incidentally, two lunar landers are set to see for this eclipse—it looks as if our planet is slowly moving in front of the sun. At first, you see Earth just barely blocking our star. The amount of light hitting you drops but not by much. Over time, Earth blocks more and more of the sun, and the illumination drops further. You’re in Earth’s shadow, yet because you can still see some of the sun, you’re not in full shadow. We call this part of the shadow the penumbra, which comes from the Latin for “near shadow.”
After about an hour, you see Earth completely block the sun. You’re in the deepest part of the shadow, called the umbra, and it is dark all around you. Eventually, Earth leaves the sun’s face—you leave the umbra and move back into the penumbra—and the ground around you is partially illuminated once again—until Earth moves completely off and the eclipse is over.
What does this look like from Earth? After all, I’d bet this is where you’ll be watching this event from! When there isn’t a lunar eclipse, if you look into the sky opposite the sun, you can’t see Earth’s shadow because it’s projected onto empty space. But if you could see the shadow, it would look like two concentric circles in the sky. The big one is the penumbra, and the smaller one inside it is the umbra. When the moon begins moving into the penumbra, it does technically get darker, but it’s hard to tell at first. Once the moon is much deeper in, its dimming becomes more obvious.
Then the leading edge of the moon (the side of it in the direction of motion, more or less to the east on the sky) drastically darkens just as it touches the umbra’s edge. As the moon moves deeper into the umbra that dark spot grows into an arc that encompasses more and more of the lunar surface. Eventually it covers more than half of the moon’s Earth-facing side, which begins to look like a crescent, until the entire moon is engulfed in the umbra. Its face becomes as dark as can be—the eclipse is total. In this period of “totality,” the moon becomes so dark, in fact, that it can be hard to find in the sky.
Astronomers divide the eclipse into several stages. First contact is when the moon’s leading edge moves into the penumbra. Second contact is when the leading edge enters the umbra; this is also the start of the partial eclipse, when Earth’s shadow falling on the moon becomes obvious. Third contact is when totality occurs. Fourth contact is when the leading edge passes out of the umbra and becomes easily visible again, ending totality, and fifth contact is when the entire moon is fully out of the umbra. Sixth contact is when the moon leaves the penumbra and the eclipse is officially over.
Remember, from the moon, the entire sun is blocked during totality. This usually creates a remarkable and eerie phenomenon from Earth: Rather than just displaying a dark, dull lunar disk, the moon’s face will instead turn bloodred. This happens as a result of the same optical physics that causes rosy sunrises and sunsets: Earth’s atmosphere scatters blue light but transmits red light, and this reddening increases as more air intervenes, like when the sun is low on the horizon. Earth is backlit by the sun during a lunar eclipse, so all the sunlight falling on the lunar surface is passing through the thickest part of our atmosphere, bathing the moon in a ruddy glow. It’s pretty cool, if a bit disconcerting.
Because the moon is in space and passes through the shadow at a specific time, the timing of all the contacts is the same for everyone in the viewing region. The only difference is your time zone. Here are the times for all the contacts in eastern daylight time (EDT):
First contact: 11:57 P.M.
Second contact: 1:09 A.M. (partial begins)
Third contact: 2:26 A.M. (totality begins)
Fourth contact: 3:32 A.M. (totality ends)
Fifth contact: 4:48 A.M. (partial ends)
Sixth contact: 6:00 A.M.
As you can see, each part takes a little more than an hour, so the entire eclipse unfolds over the whole night; if you’re on the West Coast, it’s a little easier because it starts three hours earlier on your clocks. If you want to watch the whole thing from the East Coast, you might want to take an afternoon nap because it’ll be a long night.
But it’ll be worthwhile! Watching the moon slowly swallowed by shadow is pretty amazing, and the reddish cast of totality is astonishing. You don’t need any optical aid to watch either, although I do enjoy using binoculars to get a better view.
And you never know: during the January 2019 total lunar eclipse, a small asteroid struck the moon, creating a flash that was witnessed by many people watching through telescopes live streaming the event! This is very unlikely to happen again, of course, but it was a terrific added bonus for those lucky enough to see it.
Either way, this eclipse is worth staying up for—or at least for setting a late-night wake-up alarm. It’s the only lunar eclipse that will be visible from North America this year; otherwise, you’ll have to wait until 2026, when there will be two: a total eclipse on March 3 and a partial eclipse on August 28. It’s probably your last chance for a year, so if the skies are clear and you have the time, try to take a look!
