In the mid-nineteenth century, the Harvard College Observatory began employing women as calculators, or "human computers", to interpret the observations made via telescope by their male counterparts each night. At the outset, this group included the wives, sisters, and daughters of the resident astronomers, but in the 1880s the female corps included graduates of the new women's colleges - Vassar, Wellesly, and Smith. As photography transformed the practice of astronomy, the ladies turned to studying the stars captured nightly on glass photographic plates. The "glass universe" of half a million plates that Harvard amassed in this period - thanks in part to the early financial support of Mrs. Anna Draper, whose late husband pioneered the technique of stellar photography - enabled the women to make extraordinary discoveries that attracted worldwide acclaim. They helped discern what stars were made of, divided the stars into meaningful categories for further research, and found a way to measure distances across space by starlight. Registration required.