Note: Because the lunar eclipse is something almost everyone can enjoy, I’m sending this part of the newsletter to all free subscribers as well. I hope you get a chance to look!

On Thursday night/Friday morning, August 27-28, the moon will slide almost but not quite entirely into Earth’s shadow, creating a lunar eclipse. It’s technically a partial eclipse, since the moon won’t be completely dark, but it’s very close to full, with about 93% of the moon’s diameter plunged into shadow. 

It’s a bit weird to think that Earth has a shadow, since it’s in space; we’re used to a shadow being cast onto something. But think of it this way: there is a region of space behind Earth, opposite the direction to the sun, where, if you were there, you’d see Earth blocking the sun. That’s the shadow.

It’s shaped like a looooong cone, and at the distance of the moon is about 1.5° in width, bigger than the moon’s apparent 0.5° size. The moon doesn’t pass through this area every month because its orbit is tilted to the plane of Earth’s orbit around the sun by about 5°, so usually it misses. But sometimes things line up just right and it slides right through Earth’s shadow.

From the moon’s point of view Earth blocks the sun, and from our point of view we see the moon grow dark. Because the shadow is cone-shaped, as the moon enters the shadow we see a slight circular arc cut into it. That grows and grows, like a cookie with a bigger and bigger bite taken out of it. If the moon’s trajectory is just so it’ll pass all the way into the shadow. This time, though, it only traverses the outer part, with just a little bit of its surface outside the shadow. At maximum eclipse it’ll look like there’s a thin crescent still lit. 

Unlike solar eclipses, which happen on Earth in a narrow path so you have to be at the right place at the right time, a lunar eclipse happens on the moon, so wherever you are, if the moon is up in the sky during the eclipse you can watch it. This week’s event can be seen by all the Americas, essentially all of Africa, Europe, and the Middle East. 

You can go to the terrific TimeAndDate.com website and enter your location to get your own personal viewing times. For the east coast of the US the moon starts to enter the dark part of Earth’s shadow just after 22:30. Maximum eclipse is at 00:13 (just after midnight), and the moon leaves the shadow at 01:52. That’s great timing for me; it means I don’t have to stay up super late to watch at least some of it. The farther east you are the later it all happens on your clock. For west coasters the eclipse starts just before or after moonrise, depending on your exact location.

I like lunar eclipses; they’re slow and ponderous, so you can go outside, take a look, then go back in, then head back out 15 minutes later to see the progress. It’s also fun to take a look through binoculars or a telescope to see the shadowed regions only dimly illuminated by sunlight that’s passed through Earth’s air… which is also why the moon can look red during a lunar eclipse. Speaking of which, I have way more info about lunar eclipses in general in my Crash Course Astronomy eclipse episode.

I hope you have clear skies!

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