Harvard: Honoring Henrietta Swan Leavitt
One hundred years ago, in November 1908, Henrietta Swan Leavitt created the period-luminosity law for variable stars (a star's brightness depends upon the length of its period). Her discovery was honored on November 6, 2008, at the Harvard-Smithsonian Center for Astrophysics with a series of talks from author George Johnson and various scientists. The Center is loaded with rows of cabinets containing more than 500,000 photographic plates of the stars, some of which are the very plates Leavitt used to study.
Beginning in 1893, Leavitt worked at the Harvard College Observatory, hovering over photographic plates, hunting for stars that changed in brightness over time. She was able to determine the magnitude of stars by placing a "flyspanker," or a tool calibrated to estimate brightness, on the plates. It was a lot of hard work searching through hundreds of tiny dots, but Leavitt accomplished the work with grace; she discovered 1,777 variable stars within the Large and Small Magellanic Clouds.
The Harvard College Observatory was founded in 1839 and contains a telescope veneered in mahogany, dating from 1847. The Great Refractor, as it is called, is massive: it is over twenty feet long and fifteen inches in diameter. The telescope is perched atop an 11-foot, 11-ton granite mount and is further supported by a 43-foot base, of which 23 feet lies underground. Not surprisingly, for twenty years after its installation, the telescope was the largest in the United States. The Great Refractor was primarily utilized for photometry, but it is no longer active; instead Harvard has been restoring it.
To observe with such a big telescope, an observing chair, which has been newly reupholstered, was used. It rolled on a track around the telescope, propelled by a hand crank on the seat. The lapstrake dome is thirty feet high, plated with copper, and was supposedly built by a shipwright. The dome not only contains the telescope, but other artifacts as well, such as a student transit telescope from 1897 and a chronograph from 1900.
Scientists have come a long way since Leavitt's time. The observatory now has two other telescopes--one is robotic and can be controlled from anywhere. Additionally, in the basement of the astrophysics center is a photographic plate scanner, which will digitize all of the plates collected between 1885 and 1993. A separate, conventional digital camera will also photograph the plate jackets and a collection of daguerreotypes from 1849 to 1885. The scanner photographed its first plate--an image of Rho Ophiucus from 1899--on November 21, 2005. The observatory hopes to scan the entire collection within five years.
This amazing machine has a powerful CCD camera that can scan two plates at a time in a matter of 92 seconds. The photographs are stored on two servers which hold a total of 33 terabytes of information. In order to protect the plate stacks from earthquakes, there is five feet of solid concrete beneath the floor, while the scanner rests on an air cushion to prevent it from transmitting vibrations to the rest of the building.
The purpose of digitizing the plates is to make them available to astronomers around the world via the computer. Harvard describes this fascinating project as "a new look at the temporal universe," and indeed, astronomers have certainly changed the way in which we observe space since Henrietta Leavitt.
* Find out more about the scanner.
* Watch a video of the scanner as it images two plates.