But a project at Harvard College Observatory may open allow astronomers to study how the sky changes on a 100-year timescale. Harvard hopes to digitize its collection of half a million photographic plates going back to the mid 1880s. Right now the plates are housed in an ostensibly earthquake-proof repository in Cambridge. Astronomers can access the collection as they would any specialized library archive--but it's an appointment-only, legwork-required sort of thing.
Digitizing the plates would not only make them easier to access and analyze--it would protect them from loss, breakage, and the lapses of bureaucratic reason that have historically put them at risk.
But the project is expensive. According a story in last week's New York Times, the Harvard astronomer heading up the digitization effort says a donor will have to come through with five or six million dollars to keep things afloat. From the Times' interview with Dr. Josh Grindlay:
“Somebody could easily put their name on this — the world’s first time-domain catalog....Do we really want to wait another hundred years to find out with modern instrumentation what the cosmic movie looks like? We’ve got this chance right here.”
Oh, and if you're wondering what exactly photographic plates are and what it would be like to do astronomy with them, check out Phil Plait's comments on the Bad Astronomy blog.