Annular solar eclipse seen from space

Did you know there’s going to be an annular eclipse of the sun visible from the southwestern U.S. on May 20, 2012? It reminded me of this wonderful video from Hinode, a Japanese satellite that has been orbiting Earth since 2006, of a January 4, 2011 solar eclipse – as seen from space. The eclipse was partial from Earth’s surface, but annular as seen by the satellite. Check out this video:

Whoa, yes? During this particular eclipse, as seen by lucky observers at far northerly latitudes Earth’s surface, the sun was no more than 80% covered by the moon – a partial eclipse. But Hinode was positioned so that it saw a fuller eclipse than that seen from anywhere on Earth. What’s more, as many of you already know, the sun is roughly 400 times bigger than the moon and roughly 400 times farther away – which is why the sun and moon look the same size in our sky, approximately. That’s why the moon can occasionally cover the sun completely in a total solar eclipse.

But the moon’s distance from Earth varies over its monthly orbit. For example, during the eclipse shown in this video – January 4, 2011 – the moon was in a far part of its orbit from Earth. The Earth, meanwhile, was in a near part of its orbit around the sun. So the sun looked a bit bigger than usual, and the moon looked slightly smaller.

The result was what’s called a “annular” eclipse, during which the moon cannot cover the sun completely. That’s why – at mid-eclipse – there was a bright ring, or annulus of the sun’s body, around the blackened moon.

People who are new to astronomy wonder if this video is real. We’re used to being tricked, aren’t we? Some people are worried that there’s no flickering anywhere in these images. But remember this video was taken above Earth’s atmosphere; the flickering of stars and planets in our sky comes from the fact that you’re viewing these object through Earth’s blanket of atmosphere. Also, people commented on how fast the moon moves across the sun. Yep. It’s fast. When the moon appears bigger in our sky – and the sun smaller – it takes longer for the moon to cross in front of the sun. Not so with an annular eclipse. I saw one in Alabama in the early 1980s in which the moon swept across the sun’s surface very nearly as in this video. When you are standing on the ground watching it happen in real time, you get a dramatic sense of the moon’s real, ongoing motion in space.

The moon’s speed in orbit around Earth is about 1 kilometer/second, by the way. Earth’s speed in orbit around the sun is about 30 kilometers/second. Stuff moves fast in space! We just don’t realize that, or feel it, in our everyday lives because we’re moving, too.

The Hinode satellite mission, in partnership with NASA, NAOJ, STFC, ESA, and NSC, has the goal of study the sun to improve our understanding of the mechanisms that power the solar atmosphere and drive solar eruptions that can impact hardware in orbit and life on Earth. But this satellite can awe us, too, and – for me at least – it did so with this video. Thank you Hinode!

Bottom line: There’s going to be an annular eclipse of the sun visible from the southwestern U.S. on May 20, 2012? It reminded me of a video from Hinode of another eclipse – as seen from space.

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