Search for comets through online photography

This is not a Citizen Sky project, but it may be of interest to others and it could spawn ideas for a CS team project.

The fact that they did their project on April 1 made me question whether this was an April Fools prank. This was posted on ArXiv, which is a pre-print server for scientific papers (mostly physics related). It is not refereed and sometimes silly and/or joke papers are published there. And normally I ignore all pre-print papers that are "to be submitted" which means they haven't passed a journal's referee process yet (in this case, it hasn't even been submitted). But the idea is the cool thing here and the paper is clearly and interestingly written. The authors also have bonafides in that they have previously published on this topic in a high end astronomy journal.

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http://arxiv.org/abs/1103.6038
Searching for comets on the World Wide Web: The orbit of 17P/Holmes
from the behavior of photographers
Lang, Dustin; Hogg, David W.
Abstract
We performed an image search on Yahoo for "Comet Holmes" on 2010 April 1.
Thousands of images were returned. We astrometrically calibrated---and there-
fore vetted---the images using the Astrometry.net system. The calibrated image
pointings form a set of data points to which we can fit a test-particle orbit in the
Solar System, marginalizing out image dates and catching outliers. The appro-
ach is Bayesian and the model is, in essence, a model of how comet astropho-
tographers point their instruments. We find very strong probabilistic constraints
on the orbit, although slightly off the JPL ephemeris, probably because of limita-
tions of the astronomer model. Hyper-parameters of the model constrain the re-
liability of date meta-data and where in the image astrophotographers place the
comet; we find that ~70 percent of the meta-data are correct and that the comet
typically appears in the central ~1/e of the image footprint. This project demon-
strates that discoveries are possible with data of extreme heterogeneity and un-
known provenance; or that the Web is possibly an enormous repository of astro-
nomical information; or that if an object has been given a name and photograph-
ed thousands of times by observers who post their images on the Web, we can
(re-)discover it and infer its dynamical properties!

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I love the line: "...the Web is possibly an enormous repository of astronomical information...". I think we can all agree that is an understatement written in jest. The author(s) previously posted an article to ArXiv where they stated the publication source as "a chapter in a nonexistent book". I like their sense of humor!