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upstart writes:

How an enormous project attempted to map the sky without computers:

Recently, the European Space Agency released the third installment of data from the Gaia satellite, a public catalog that provides the positions and velocities of over a billion stars. This is our most recent attempt to answer some of the most long-standing questions in astronomy: How are stars (and nebulae) spread out across the sky? How many of them are there, how far away are they, and how bright are they? Do they change in position or brightness? Are there new classes of objects that are unknown to science?

For centuries, astronomers have tried to answer these questions, and that work has been laborious and time-consuming. It wasn't always easy to record what you could see in your telescope lens—if you were lucky enough to have a telescope at all.

Now imagine the emergence of a new technique that, for its time, offered some of the benefits of the technology that enabled the Gaia catalogs. It could automatically and impartially record what you see, and anyone could use it.

That technique was photography.

This article tells the story of how photography changed astronomy and how hundreds of astronomers formed the first international scientific collaboration to create the Carte du Ciel (literally, "Map of the Sky"), a complete photographic survey of the sky. That collaboration resulted in a century-long struggle to process thousands of photographic plates taken over decades, with the positions of millions of stars measured by hand to make the largest catalog of the night sky.

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