Saturday’s Entire Lunar Eclipse in One Minute

On Saturday, the Moon very briefly slipped into the Earth’s shadow, creating a total lunar eclipse. It was the shortest total eclipse this century, with totality lasting just under five minutes.

I saw lots of lovely pictures from the event, but I think my favorite is a time-lapse video taken at Griffith Observatory in Los Angeles, sent to me by my friend and astronomer Laura Danly. They kept the telescope centered on the Moon, and you can watch the whole eclipse in just seconds:

There are a couple of cool things you can see in the video.

The Earth casts two shadows in the sky. One is a wide, faint shadow called the penumbra; when the Moon is in that part, the Sun is still visible from the Moon but partly blocked by Earth. The Moon gets fainter, but not really dark. Centered in that shadow is the darker umbra, and it’s obvious when the Moon slips into that part. From inside the umbra, the Sun is completely blocked by the Earth.

You can see the curved edge of the umbra move across the Moon (though it’s probably more accurate to say the Moon moves into it). Since the Moon’s path took it on a narrow chord across the northern portion of the umbra, the eclipse was very short, and barely total. Here’s a diagram showing this:

The other thing that I found interesting was the jumpy nature of the shadow. Shouldn’t it move smoothly? And why does it appear to jump backward?

Well, it did move smoothly, and never actually moved backward! What was happening is that as more of the Moon was covered, the exposure times of the camera were changed to compensate. A longer exposure made the edge of the shadow look lighter, so it appears to jump backward in two successive frames, even though it’s actually moving forward. It’s not real movement, it’s just the exposure tricking your eye into thinking that.

Pretty nifty. There’s another lunar eclipse on Sept. 28 of this year, so I expect we’ll see more pictures and fun videos of that event, too. Mark your calendar!

And if you want to learn more about eclipses, may I suggest watching the Crash Course Astronomy episode on them?

Correction, April 6, 2015, at 16:30 UTC: The wrong video was originally embedded in this post due to a new YouTube functionality that starts playing new videos once one finishes—I didn't notice when I grabbed the URL to embed. My apologies.