HARVARD COLLEGE OBSERVATORY / SCIENCE PHOTO LIBRARY HARVARD COLLEGE OBSERVATORY / SCIENCE PHOTO LIBRARY
The US astronomer Henrietta Leavitt (1868-1921). She graduated from Radcliffe College in 1892 and joined the Harvard College Observatory in 1895. Her studies on the photographic magnitudes of stars led her to the discovery of the Cepheid variables in the Magellanic Clouds. She also noticed that the brightness variation in the Cepheids was extremely regular, and that the brighter stars had longer periods. By 1912, she had established that the apparent magnitude varied as the logarithm of the period. This was the foundation of the method now used to measure extreme cosmic distances.
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