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lith1x t1_j3fo394 wrote

What causes the star trails? Is it the rotation of the ISS..?

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whiskysinger t1_j3fzhrd wrote

Yes - it is exactly the same mechanism as the star trails taken from Earth's surface. Except the ISS is orbiting much quicker than the Earth is rotating. This is why the trails in this photo are so long for such a short exposure*.

Interestingly, the celestial pole is different on the iss than what we are used to on earth (Polaris in the northern hemisphere) because the orbital axis is not the same as Earth's axis of rotation, as demonstrated in the gif below.

https://gfycat.com/meagerscientificbengaltiger

*The ISS takes 90 minutes to orbit the earth. This means it is completing one trip around its orbital axis 16 times per earth day. The photo took 65 seconds of exposure. To capture star trails of this length on earth would take 16 x 65 seconds = 1040 seconds = 17m20s of exposure. (I think! Please correct me if I'm wrong)

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astro_pettit OP t1_j3osr8p wrote

Thanks for taking the time to answer; the physics behind the motion is different than what an Earth centric star trail would make you think.

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