The Sciences

Amazing moonset video taken from space!

Bad AstronomyBy Phil PlaitJan 31, 2012 11:32 PM


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[Set it to high-def and make it full screen!] Astonishing, isn't it? As the Moon sets, you're seeing it through thicker and thicker air. The air acts like a lens, bending the light upward. The part of the Moon nearer the Earth's limb gets bent up more, so the Moon looks like it's getting flattened. Watch it again; the top of the Moon doesn't appear to be affected much. It looks more like the bottom slows down and the top pushes into it. You can read about this effect in more detail in an earlier blog post


Weirdly, as I watched the video, it looked very much like the whole Moon was shrinking as it set, as if it were receding rapidly. When I saw that I knew intuitively that couldn't be real; the ISS is only moving a few thousand kilometers over the time this whole video was taken (about ten minutes), not nearly enough to see that big a change in the size of the Moon. It's 400,000 kilometers away, after all! So I measured the size of the Moon on the screen, and incredibly the width doesn't change. Do you see it appear to shrink too? It's an illusion! Funny how our brain interprets such things. As if seeing a gigantic rock moving through the sky while perched on board a football-field sized satellite moving at 30,000 km/hr isn't weird enough!


Related posts: - The Moon is flat! - The twice reflected Moon light - Incredible time lapse: Milky Way over Africa

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