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Another look at the green comet

Here's a little bonus astrophotography post for you. This is the same star trails picture that I put up a few weeks ago, but while I was messing around recently on the NASA site I realized that it probably showed something interesting. And it does:

I grayed out the image except for the part I've pointed to. In a normal star trails photo, the trails are circular because they're a result of the rotation of the earth against a motionless sky. However, comets have some motion of their own, which makes their trails slightly non-circular. And sure enough, if you look closely at the trail I pointed to,¹ it's not quite concentric with the one to its right. This is a sign that it's a comet, not a star.

¹As always, click to embiggen!

10 thoughts on “Another look at the green comet

  1. gs

    That is the cleanest "spot the comet" trick I've ever seen. The green is nowhere near as obvious as the color in some of the other objects for some reason ...

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