The Pisgah Astronomical Research Institute (PARI) is home to the Astronomic Photographic Data Archive (APDA), a collection of photographic plates taken by optical telescopes from the mid-19th century through the late-20th century. Some of these plates are the only existing documentation of astronomic features that are no longer there. All of them represent shots of the night sky before the advent of "space junk."
It's an amazing project, and one that citizen scientists can get involved in as well. Through SCOPE—Stellar Classification Online Public Exploration—you can get a good look at the plates in the APDA archive and help professional scientists document and classify all the stars depicted in them.
Maggie Koerth-Baker is the science editor at BoingBoing.net. She writes a monthly column for The New York Times Magazine and is the author of Before the Lights Go Out, a book about electricity, infrastructure, and the future of energy. You can find Maggie on Twitter and Facebook.