Observing The Past

The Harvard College Observatory, home to half a million glass photographic plates of the night sky from over 100 years of observations, is currently in the midst of one of the greatest preservation efforts in astronomical history.

But faculty at the observatory hope that making high-resolution digital copies of all the plates—a project slated to take five years—will also help modern astronomers as they probe current mysteries of the universe through a detailed look into the past.

“This is all going to be public information,” said Alison Doane, the curator of the three floors of cramped stacks at the observatory. “Anyone in the world will essentially be getting a century’s worth of free telescope time.”

Doane put the price tag of the project over the next five years at roughly $5 million.

“But I say five years with a bit of a smirk,” she said. “You know you’re going to have some problems when you have so many plates and you need so much accuracy.”

A CENTURY’S WORTH OF SKY

The one-of-a-kind scanner used to digitize the plates was built piecemeal, largely by volunteers and workers at the observatory, and will be able to take 120 photos of two small plates—each measuring 8-by-10 inches—in just over a minute.

The special calibration software designed specifically for this project will then stitch the photos together and create a large image accurate to lengths of less than one micron.

Jeffrey J. Blair ’09, an astronomy concentrator, said that without this project, the plates would be almost useless to modern astronomers.

“But as soon as these things are opened up, basically every field of astronomy is going to be able to use it some extent,” Blair said. “The most important thing for modern research is to have a set of data of a specific area of sky over a long period of time.”

Blair said he also hopes this project will open up important research opportunities to undergraduates.

“No professor is going to spend $5,000 of his grant to give an undergrad a night on a telescope,” he said. “But with this data, you could conceivably be doing research as a freshman that would turn into a publishable paper.”

Paine Professor of Practical Astronomy Jonathan E. Grindlay also stressed the scientific importance of this preservation effort.

“I’d estimate that only about one percent of the information here has ever been looked at,” said Grindlay, the principal investigator in this project.

“To do the types of comparisons that we’ll be able to do once this project is completed would be an astronomical task if attempted by hand,” he said. “But if you have it in digital form, you’re opening up a whole new world.”

Grindlay said he hopes the plates will be able to shed more light on many astronomers’ favorite new mystery objects—quasars, the super-massive black holes that form the center of many galaxies.

“These quasars are spectacularly variable, bubbling and flickering and doing all sorts of wonderful things,” Grindlay said. “But the most massive ones vary on time scales of months or even years, and not many data sets have that kind of sky coverage.”

Harvard’s collection of plates is the largest in the world both in terms of length of time covered—the plates record over a century’s worth of sky dating from the 1880s to the 1990s—and in terms of breadth, as the plates provide images of the sky from both the northern and southern hemispheres.

Doyle Professor of Cosmology John P. Huchra also emphasized the importance of being able to examine sky variability over long periods of time.

“One of the new frontiers in astronomy, with the exception of extrasolar planets, is really the time domain,” Huchra said. “When you’re trying to understand how things have changed, rarely do you get to go back and look at the same place over and over again.”

According to Huchra, this project—the Digital Access to a Sky Century at Harvard (DASCH)—would provide just such an opportunity.

OUT OF SPACE?

But DASCH has already faced significant setbacks.

Creating a completed digital picture of a plate with all the necessary file backups takes about two gigabytes of hard drive space.

And while Doane said that the DASCH team is excited that it created a server that can hold 13 terabytes of data—13,000 gigabytes—for only $12,000, photographing all the plates will require more than 70 times as much memory.

Funding has also recently become an issue, as the observatory has always used grant money to pay its staff salaries and provide for the building’s upkeep.

Doane said they were close to getting a grant for the project through Harvard’s Library Data Initiative, a program that started in 1998 to promote an increase in quality of Harvard Library’s digital information, but the application fell through over disagreements on where and how to store the data.

For now, though, the team is trying to stay optimistic, focusing instead on the discoveries that could follow from their project’s completion.

“I can still remember thinking, back when I was a grad student and looking at some of the plates the old fashioned way, ‘Wow, what a treasure trove of data,’” Grindlay said. “And now we’ll be able to use it all.”

—Staff writer Nathan C. Strauss can be reached at strauss@fas.harvard.edu.