This Sunday night, May 15, the Moon will totally venture into the Earth’s shadow, producing our area’s first worthwhile eclipse in several years. As we recounted in last week’s issue of Hudson Valley One, it’s really the appetizer, the warm-up to a series of eclipses that will culminate in the astounding 2024 solar total eclipse visible just a four-hour drive north of here.
First things first. If it’s clear Sunday evening, start watching the full Moon at around 10:30. It’ll be in the southeast in the constellation Libra, and at that hour you might already see a strange if subtle unevenness in its brightness. But the first dramatic, in-your-face alteration occurs at 10:38. A tiny but steadily growing black “bite” will appear on the Moon’s left side. Binoculars may make it a bit more impressive, but in truth you need no optical assistance for a lunar eclipse.
During the next hour, the black “bite” grows ever-larger, and it’s fascinating to accurately picture it for what it is — our planet’s shadow. Earth is four times the Moon’s diameter, but our dark umbral shadow tapers like a chopstick to be only about half its original size by the time it reaches the Moon’s distance of nearly a quarter-million miles. So the shadow’s curvature is an arc of a circle that’s much bigger than the Moon. Since lunar eclipses always happened when the Moon was precisely opposite the Sun in our sky, the ancient Greeks concluded that Earth must be round, and such events even revealed our size to those who were particularly smart, like Aristarchus on the island of Samos.
So Sunday night is a good time to phone any flat-Earth acquaintances, since this eclipse is visible from everywhere in the US and Canada. One of them might try to lamely counter that Earth is still flat, but merely shaped like a disk or dish. But you’ll have your reply ready: A dish usually casts an elliptical shadow, or even one that’s a dark straight-line. Only a sphere always throws a round shadow!
Another cool fact is that, as you watch, it takes the Moon one hour and one minute to fully enter our shadow, revealing that it moves through space one Moon-width an hour. Since the Moon is 2,160 miles in diameter, that’s its hourly velocity, a real slowpoke compared with Earth’s speed of 66,600 mph. The Moon is the only celestial body that moves its own diameter per hour.
During that hour, watch as the shadow slowly metamorphoses from black to coppery red. The strangest appearance and my favorite time to see this event will happen around 11:15 or 11:20 p.m., when only a small bit of sunlight still hits the Moon while the rest of it looks deliciously orange. The scene is reminiscent of the planet Mars with its polar cap.
What’s that color? Glad you asked. Turns out, our planet’s shadow is coppery-red, not black. You’d see why if you were an astronaut on the Moon at that time. You’d see the inky black Earth with the much smaller-looking Sun hidden behind it. But surrounding Earth is a ring of reddish light, which is all of Earth’s sunrises and sunsets merged into a single gorgeous halo. It’s that light alone that now bathes the lunar terrain. But as you’ll see, it’s not a “blood red” color, which is why the newly-minted term “blood Moon” is a poor title for a lunar totality.
Totality begins at 11:28 and lasts an hour and a quarter. But unlike solar eclipses whose totality brings strange and wonderful phenomena that make it life’s most glorious sight, absolutely nothing happens during lunar totality. The full Moon is now coppery red and usually a bit brighter on one side, and an abundance of faint stars that were masked by the full Moon’s brilliance earlier in the night now flood the sky if you’re away from city lights.
But nothing else happens. So at some point — usually after five, ten, or twenty minutes — you’ll go back inside and call it a night. A good night indeed.