LOS ANGELES, CA (Catholic Online) - "The Harvard College observatory has the most wonderful, best collection [of photographic plates] in the world," Harvard graduate student Sumin Tang says. Tang, who works on the plate analysis program says that it is "a very unique resource because it's over 100 years. No other data set could do this."

The plates were created at a time when researchers used glass surfaces coated with light-sensitive silver salts to record discoveries seen by telescopes. The Harvard collection includes plates made with dozens of telescopes.

Beginning in the 1990s, photographic plates were replaced with more sensitive CCDs, or charge-coupled devices, which are digital light sensors. Smaller versions of these same devices power digital cameras.

Scientists are now trying to digitize the plate collection, basically using CCDs to image the plates. The scientists then apply an algorithm to quantify how bright stars appear and search for variations over time. Called Digital Access to a Sky, the project is headed by Harvard astronomer Jonathan Grindlay.

"In this way we can perform a systematic search for long-term variables," Tang says. "We don't need to use our eyes, because it would take forever."

The majority of the stars in the plate collection were imaged between 500 and 1,500 times. The images provide ample evidence for some weird stellar behavior. Only four percent of the plates thus far have been digitized, but that data set alone has turned up some new discoveries. The team hopes to digitize the whole collection over the next three to five years.

The initial data has yielded some "wonderful results," Tang said. Some of the stars caught on the plates brighten and dim gradually for reasons unknown. "We've found several different new types of variables," she added.

Astronomers have discovered a group of stars that all vary in the same, weird way. These stars all happen to belong to a class called K giants, with temperatures of about 47,500 degrees Fahrenheit. Over decades they become brighter and dimmer by a factor of two.

"This kind of timescale is weird because it's just too long," Tang said.

The researchers think the stars can actually be divided into two classes: binary (double star) systems, and single stars, with two different mechanisms behind their variations.

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