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The Sciences

Squishy moonrise seen from space!

Bad AstronomyBy Phil PlaitJanuary 21, 2011 10:30 PM

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Check. This. Out: Moonrise as seen by astronaut Paolo Nespoli on board the International Space Station!

iss_moonrise_jan2011.jpg

Holy wow! Click to spacestationate. That is so cool. As the ISS races around the Earth at 8 km/sec (5 miles/sec), it sees up to 18 sunrises and sunsets each day, and the same number of moonrises and moonsets. Paolo had to snap quickly to get this sequence, which couldn't have taken more than a minute to elapse. But what's with the squished Moon? Here's a closeup of the Moon in the three pictures:

iss_moonrise_jan2011_crop.jpg

What causes this? It's an atmospheric effect, due to the air surrounding the Earth acting like a lens, bending (or, if you want to impress your friends, refracting) light. You've probably seen how a spoon looks bent when it sits in a glass of water, right? Same thing. Light passing from the vacuum of space through our air gets bent a bit. The amount of bending depends on how much air the light is going through; the thicker the air the more it's bent.

iss-moon_los_300.jpg

When an astronaut on the ISS sees the Moon near the Earth's limb, as in these shots, light from the top part of the Moon is passing through less air than the bottom. So the light from the bottom gets bent more, in this case, up. This makes it look as if the bottom of the Moon is being squished up into the top, like a clay ball that's been dropped on the ground. As the ISS orbits the Earth, and the Moon gets higher off the limb, the effect diminishes so in the two subsequent shots the Moon gets re-inflated. You've probably seen this yourself, though not as dramatically. The next time you have a clear horizon view to a sunset (like maybe on the west coast, as the Sun sinks below the waters of the Pacific) you'll see exactly this same effect. The Sun will look squashed. I've actually posted about this a couple of years ago, when a similar picture of the Moon from the ISS was released. It wasn't as dramatic as this one, though! Paolo Nespoli has a Flickr page where he posts amazing pictures he's taken from space. You could have a much worse Friday than clicking through some of those shots and seeing how lovely our world is when seen from above.

Image credit: ESA/NASA. Tip o' the spacesuit visor to Stuart at astronomyblog.

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