Harlow Shapley (November 2, 1885 – October 20, 1972) was an American astronomer, who served as head of the Harvard College Observatory from 1921–1952, and political activist during the New Deal and Fair Deal. Shapley used Cepheid variable stars to estimate the size of the Milky Way Galaxy and the Sun's position within it. In 1953 he proposed his "liquid water belt" theory, a concept now known as a habitable zone.
Background
Shapley was born on a farm five miles outside Nashville, Missouri, to Willis and Sarah (née Stowell) Shapley. He went to school in Jasper, Missouri, but not beyond elementary school. He worked as a journalist after studying at home and covering crime stories as a newspaper reporter for the Daily Sun in Chanute, Kansas, and intermittently for the Times of Joplin, Missouri. In Chanute, he found a Carnegie library and started reading and studying on his own. Shapley returned to complete a six-year high school program in 1.5 years, graduating as class valedictorian. In 1907, Shapley went to the University of Missouri to study journalism. When he learned that the opening of the School of Journalism had been postponed for a year, he decided to study the first subject he came across in the course directory. Rejecting Archaeology, which Shapley later claimed he could not pronounce, he chose the next subject, Astronomy.
Early years After graduation, Shapley received a fellowship to Princeton University for graduate work, where he studied under Henry Norris Russell and used the period-luminosity relation for Cepheid variable stars (discovered by Henrietta Swan Leavitt) to determine distances to globular clusters. He was instrumental in moving astronomy away from the idea that Cepheids were spectroscopic binaries, and toward the concept that they were pulsators. He realized that the Milky Way Galaxy was far larger than previously believed, and that the Sun's place in the galaxy was in a nondescript location. This discovery supports the Copernican principle, according to which the Earth is not at the center of the Solar System, the Milky Way galaxy, or the Universe.
The Great Debate of 1920 Shapley participated in the "Great Debate" with Heber D. Curtis on the nature of nebulae and galaxies and the size of the Universe. The debate took place on April 26, 1920, in the hall of the United States National Academy of Sciences in Washington DC. Shapley took the side that spiral nebulae (what are now called galaxies) are inside the Milky Way, while Curtis took the side that the spiral nebulae are "island universes" far outside the Milky Way and comparable in size and nature to the Milky Way. This issue and debate are the start of extragalactic astronomy, while the detailed arguments and data, often with ambiguities, appeared together in 1921. Characteristic issues were whether Adriaan van Maanen had measured rotation in a spiral nebula, the nature and luminosity of the exploding novae and supernovae seen in spiral galaxies, and the size of the Milky Way. However, Shapley's actual talk and argument given during the Great Debate were completely different from the published paper. Historian Michael Hoskin says "His decision was to treat the National Academy of Sciences to an address so elementary that much of it was necessarily uncontroversial", with Shapley's motivation being only to impress a delegation from Harvard who were interviewing him for a possible offer as the next Director of Harvard College Observatory. With the default by Shapley, Curtis won the debate. The astronomical issues were soon resolved in favor of Curtis' position when Edwin Hubble discovered Cepheid variable stars in the Andromeda Galaxy. At the time of the debate, Shapley was working at the Mount Wilson Observatory, where he had been hired by George Ellery Hale. After the debate, however, he was hired to replace the recently deceased Edward Charles Pickering as director of the Harvard College Observatory (HCO).
Conversion to Hubble's ideas He is also known to have opposed Edwin Hubble's observations that there are additional galaxies in the universe other than the Milky Way. Shapley fiercely critiqued Hubble and regarded his work as junk science. However, after he received a letter from Hubble showing Hubble's observed light curve of V1, a Cepheid variable star in the Andromeda galaxy, he withdrew his criticism. He reportedly told a colleague, "Here is the letter that destroyed my universe." He also encouraged Hubble to write a paper for a joint meeting of the American Astronomical Society and American Association for the Advancement of Science. Hubble's findings went on to fundamentally reshape the scientific view of the universe. Despite having earlier argued strongly against the idea of galaxies other than the Milky Way, Shapley went on to make significant progress in the research of the distribution of galaxies, working between 1925 and 1932. In this time period, with the Harvard College Observatory, he worked to map 76,000 galaxies. One of the first astronomers to believe in the existence of galaxy superclusters, Shapley later discovered a large and distant example, which was later named the Shapley Supercluster. He estimated the distance to this supercluster at 231 Mpc, which is within 15% of the currently accepted value.
Harvard College Observatory He served as director of the HCO from 1921 to 1952. During this time, he hired Cecilia Payne, who, in 1925, became the first person to earn a doctorate at Radcliffe College in the field of astronomy, for work done at Harvard College Observatory. From 1941 he was on the original standing committee of the Foundation for the Study of Cycles. He also served on the board of trustees of Science Service, now known as Society for Science & the Public, from 1935 to 1971.
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