Female astronomers connected the dots

When Harvard president Lawrence H. Summers suggested that there might be ''innate" differences between women and men that affect their success in the sciences, it brought to mind an extraordinary story concerning women scientists at Harvard at the start of the 20th century.

In 1877, Edward Pickering became director of the Harvard College Observatory and initiated a relentless program of photographing the night sky. The observatory would take a half-million photographic plates in the decades to come, so one of Pickering's biggest challenges was to establish an industrial-scale system for analyzing them. Each plate contained hundreds of stars, and each speck would need to have its brightness evaluated and its location measured.

Pickering, who led the observatory for 42 years, recruited a team of young women to act as computers, a term originally used to describe people who manipulated data and performed calculations. It was menial work in a field of research from which women were otherwise excluded. It was then unthinkable that women would be allowed to stay up through the night staring through telescopes in the freezing cold.

Nevertheless, these mostly untrained women (known as "Pickering's harem") were able to make an enormous contribution to astronomy. They had brilliant minds and gained an intimate knowledge of the data, so they were able to make astounding discoveries.

For example, Williamina Fleming was a single mother struggling to survive when she became an employee at the observatory in 1879, but she went on to find 10 of the 24 novas then known.

Annie Jump Cannon made a major contribution to stellar classification, establishing a system that, with only minor modifications, is still in use. She divided stars into seven classes -- O, B, A, F, G, K, M. Today's undergraduates learn these stellar classifications according to the mnemonic ''Oh, Be A Fine Girl -- Kiss Me!"

In 1925, Cannon became the first woman to receive an honorary doctorate from Oxford University. She also was voted one of the 12 greatest American women in 1931, and the same year became the first woman to receive the prestigious Draper Gold Medal from the American National Academy of Sciences.

Cannon had been struck down by scarlet fever as a child, which left her almost deaf. The most famous member of Pickering's harem, Henrietta Leavitt, was also profoundly deaf. Leavitt was born in 1868 in Lancaster. In 1892, she graduated from Harvard University's Radcliffe College, and later went on to become a volunteer at Harvard College Observatory. She spent several years sifting through the photographic plates searching for variable stars, which she had been asked to catalog. Variable stars, as the name suggests, have the unusual property of growing brighter and then fading over the course of a few nights or a few weeks. Leavitt would discover more than 2,400 variable stars, about half of the total known in her day. Professor Charles Young of Princeton University was so impressed that he called her ''a variable-star fiend."

Of the different types of variable stars, Leavitt developed a particular passion for so-called Cepheid variables. After months spent measuring Cepheid variables, she realized that it would be possible to work out the actual brightness of a Cepheid variable star based on how quickly it went from bright to dim and back to bright again. Astronomers previously did not know if a star was dim and close up or bright and far away, but Leavitt could answer this question with respect to Cepheids.

This was an incredible breakthrough because, once Leavitt had shown astronomers how they could measure the actual brightness of Cepheid variables, it enabled them to measure the distances to these stars and to effectively measure the distances across the cosmos.

Leavitt's discovery transformed astronomy and ultimately laid the foundations for men like Edwin Hubble to find the first evidence in favor of the big-bang model of the universe.

While Hubble and other successful male astronomers gained great fame, Leavitt and her colleagues largely have been forgotten.

Simon Singh is the author of ''Big Bang," a history of cosmology.