Smithsonian Astrophysical Observatory - 2010 Feb 26
Modern astronomy sometimes makes discoveries by looking in new places, the distant universe for example, using telescopes and instruments that extend the previous limits of detection. But sometimes new discoveries can come from applying modern technologies to the task of more carefully examining conventional data.
The Harvard College Observatory maintains a collection of more than 500,000 glass photographic plates of the sky taken over a century - from between about 1880 and 1980. They constitute the only continuous record of the whole sky in existence for this period, with every point on the sky having been observed between 500 and 1000 times. The Digital Access to a Sky Century at Harvard (DASCH) is a project now underway to digitize all of these plates and search for changes. In one of the first results of this ongoing program, a new class of variable stars has been discovered.
CfA astronomers Sumin Tang, Jonathan Grindlay, and Edward Los, together with a colleague, used the first results of the DASCH project to discover three objects in what appears to be a new class of variable stars that change in optical brightness (both dimming and brightening) by more than a factor of two over a timescale of 10-100 years.