Greatest astronomer, help for a research paper

A TVA member recently asked Who is the greatest astronomer of all time? Criteria is wide open.
It is difficult to choose a greatest astronomer. One can start by comparing what various astronomers did with the equipment they had. For example, Tycho Brahe did his work before the telescope, and his data were used by later astronomers. Even Hipparchus, from ancient Greece, managed to figure out that Earth precesses. This was quite a feat for the time. Not long ago I read a book of the discovery of parallax. The astronomer who solved the problem, I recall, had to evade conscription into Napolean's army. Another example of rising above the times.
Another TVA member wrote: "The greatest observer was William Herschel. Nobody else is even close. He discovered Uranus, the first planet beyond the classical five (plus Earth) that had been known since humans first looked up from the savannahs of Africa. In addition, Herschel observed and recorded thousands of deep-sky objects. His list formed the basis of the New General Catalogue, or NGC, which is still the basic set of objects investigated by both professional astronomers and amateurs. His sister, Caroline, should receive some joint recognition, since it was she who wrote down his observations as he teetered on a ladder at the eyepieces of his homemade reflectors. The most important astronomer was Galileo Galilei. Probably someone else -- probably someone did -- would have turned a telescope to the sky, but he's the one who did it and simultaneously had the scientific awareness to write down his observations. With his first few observations, Galileo overturned thousands of years of superstition and speculation and started mankind on the road to learning what's really up there."
In addition, I would add this article from Nature:
http://www.nature.com/news/2009/090206/full/news.2009.81.html
The article also mentions using citation as a metric. Many theories get published, but knowing what is current and valuable requires some sense of the amount of citation it gets in credible publications. The scientific community follows the citations, but the popular media and public often don't, which leads to common misconceptions on certain topics (e.g., global warming and evolution).