Glass Astronomy 
Just about every observatory has one: A storage space filled with glass plates. For a century, they were the highest of astronomical technology. They recorded images of the universe, and the spectra of countless stars and galaxies.
One of the biggest collections is at the Harvard College Observatory in Cambridge, Massachusetts. Three floors of the observatory hold half a million plates, weighing in at 170 tons. They were snapped through telescopes in the northern and southern hemispheres, from the late 1800s to the late 1900s.
And they contributed to some of the most important astronomical work in history. Annie Jump Cannon used the plates to develop a classification system for stars, plus a giant star catalog, that are still in use today. And Henrietta Leavitt used them to discover a way to measure the distances to other galaxies.
Today, astronomical observations are recorded electronically. But the Harvard plates remain a valuable resource, particularly for studying objects that change over time -- stars that vary in brightness, or the remnants of dying stars that are expanding into space.
So Harvard is in the middle of a years-long effort to digitize the plates for future generations of astronomers. It's required a specially designed scanner and lots of hard work. But the reward will be a catalog of millions of objects -- kept fresh under glass.
We'll talk about efforts to preserve more astronomical history tomorrow.
Script by Damond Benningfield, Copyright 2011