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SYFY WIRE Bad Astronomy

The Comet and the Cosmic Beehive

By Phil Plait

In mid-October, the comet C/2013 A1 (Siding Spring) will have a very close encounter with Mars. It will pass just over 130,000 kilometers from the Red Planet; while engineers have been working to make sure our spacecraft are safe from debris, scientists are eager to gather data about the comet using those same spacecraft.

In the meantime, the comet has become a favorite for astrophotographers, because it’s relatively bright and has been passing by one astronomical gem after another. Marco Lorenzi is one such astrophotographer. He has a remotely operated observatory outside of Coonabarabran, Australia, and on Aug. 30, 2014, took this stunning shot of the comet as it passed by one of the most beautiful objects in the sky: the globular cluster 47 Tuc.

Crikey! 47 Tuc is one of the largest globulars in the sky, a million or so stars packed into a sphere held together by their own gravity. You can spot a few other clusters dotting the images as well.

Lorenzi had to be a bit tricky to get this shot. The cluster requires long exposures, but during those the comet moves so much it would get smeared out. So he took a series of long exposures for the cluster and short ones for the comet, combining them in such a way that it faithfully represents what the scene looked like (the method he used is outlined here). Clever.

And, of course, quite beautiful. Incredibly, I had to shrink it to fit the blog; click it for the full 2,200 x 2,200 version. And even then, Lorenzi told me this is only a small part of the full frame he took! Yikes.

I suspect I’ll be running more pictures by him in the future, because wow. In the meantime check out some of the other amazing pictures he’s taken. You won’t regret it.

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