For a short time back in October 2007, Comet 17P/Holmes became the largest object in the Solar System as the thin ball of dust and gas that surrounds it briefly became larger than the Sun. At the same time, Holmes brightened by a factor of half a million, making it visible to the naked eye. (All this activity seems to have been caused by a sudden outburst of gas from the comet’s nucleus.)

This sudden brightening triggered a huge wave of interest from astrophotographers all over the world, many of whom posted their images on the web. To find out how many, Dustin Lang from Princeton University in New Jersey and David Hogg at the Max-Planck-Institut fur Astronomie in Heidelberg, Germany, searched the web. They found 2476 different shots of Holmes.

That’s a significant astronomical database that represents a huge amount of work. But is it any use?

Today, Lang and Hogg use these images to work out an accurate orbit of Comet 17P/Holmes, a significant achievement given that the data is taken from an ordinary web search and its provenance is entirely unknown.

The method is relatively straightforward. These guys fed each image into the astrometry.net website which analyses the pattern of stars in the shot and then tells you which part of the sky it shows.

They then created a giant montage of these images, carefully superimposing the stars. Since the pictures were all taken at different times, the superimposed images show the comet moving across the sky (see image above).

They then compared the comet’s trajectory with the orbit calculated by the Jet Propulsion Laboratory, finding a remarkably close match.

That’s an impressive piece of crowdsourcing. All the more so because it differs in one very important way from the various other crowdsourcing projects on the go, such as GalaxyZoo. None of the astrophotographers who took these shots knew they were taking part and most still don’t.

More impressive still is Lang and Hogg’s assertion that this is only the beginning for this kind of data mining. “We have only scratched this surface,” they say.

The big question that concerns them is how far it is possible to take this data mining technique.They say there is a similar body of images for Comet Hyakatuke and have begun an analysis of these. And they point out that there are more than 3500 images of the Orion Nebula on Flickr alone.

They conclude by asking whether it might be possible to use the collected images of the world’s astrophotographers to carry out a survey of the entire night sky. “We expect the answer is yes,” they say.

We’ll look forward to seeing it.

Ref: arxiv.org/abs/1103.6038: Searching For Comets On The World Wide Web: The Orbit Of 17P/Holmes From The Behavior Of Photographers

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