Harlow Shapley

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American astronomer (1885–1972)

Shapley came from a farming background in Nashville, Missouri. He began his career as a crime reporter on the Daily Sun of a small Kansas town when he was 16. He entered the University of Missouri in 1907 intending to study journalism but took astronomy instead, gaining his MA in 1911. He then went on a fellowship to Princeton where he studied under Henry Russell and gained his PhD in 1913. From 1914 to 1921 he was on the staff of the Mount Wilson Observatory in California. Finally Shapley was appointed in 1921 to the directorship of the Harvard College Observatory where he remained until 1952, also serving for the period 1922–56 as Paine Professor of Astronomy.

Shapley's early work, under Russell, on eclipsing binaries proved that the group of stars, known as Cepheids, were not binary but were single stars that changed their brightness as they changed their size. Cepheids were thus the first ‘pulsating variables’ to be discovered, the theory of the pulsation being supplied subsequently by Arthur Eddington.

Once at Mount Wilson, Shapley began to study Cepheids in globular clusters, huge spherical groups of closely packed stars. From this stemmed his fundamental work on the size and structure of our Galaxy. In 1915 he was able to make a bold speculation about the galactic structure. Using the relation between the period of Cepheids and their observed brightness, discovered in 1912 by Henrietta Leavitt, he was able to map the relative distances of clusters from us and from each other. To his surprise he found that they were widely and randomly distributed both above and below the plane of the Milky Way and appeared to be concentrated in one smallish area in the direction of the constellation Sagittarius. He argued that such a distribution would make sense if the Galaxy had the shape of a flattened disk with the clusters grouped around the galactic center. This required that the solar system be displaced from its accepted central position by a considerable distance.

Thus Shapley had found the general structure of the Galaxy but not its size. Here the Cepheids were of limited use as they could only provide a relative scale. Absolute distances could at that time only be determined for small distances. In order to calibrate his galactic structure Shapley needed to measure the distance of a few Cepheids. He used a statistical method pioneered by Ejnar Hertzsprung in 1913. Since the intrinsic brightness, or luminosity, of stars can be determined once their distance is known, Shapley's measurements allowed him to produce a quantified form of the relationship between Cepheid period and observed brightness, i.e., a period-luminosity relationship. This P-L relationship meant that a measure of the period of any Cepheid would reveal its luminosity and hence its distance and the distance of the stars surrounding it.

By 1920 Shapley felt that he had finally cracked the fundamental problem of the scale of the Galaxy. The Sun, he declared, was some 50,000 light-years from the center of the Galaxy while the diameter of the galactic disk could be perhaps 300,000 light-years. Actually Shapley's calculations were too generous as he was unaware of the interstellar matter that absorbs some of the light from stars and thus affects determinations of stellar brightness. Consequently his figures were later revised to 30,000 light-years for the distance to the galactic center and 100,000 light-years for the diameter.

Shapley was however less successful with his work on the scale of the universe. In 1920 he took part with Heber Curtis in a famous debate organized by the National Academy of Sciences at the Smithsonian in Washington. Using the brightness of novae in the Andromeda nebula, Curtis gave an estimate approaching 500,000 light-years for its distance and maintained that it was an independent star system. Shapley, misled by the measurements of Adriaan van Maanen, argued that this distance was far too great and that the Andromeda nebula and the other spiral nebulae lay within the Galaxy. It was left to Edwin Hubble to show, some years later, that Curtis had in fact underestimated rather than overestimated the distance of the Andromeda nebula and that it was in fact a separate star system.

Not the least of Shapley's achievements was his development of the Harvard Observatory into one of the major research institutions of the world. He introduced a graduate program and attracted a distinguished and much increased permanent staff. During his time there his interest turned to ‘galaxies’, as he called them, or ‘extragalactic nebulae’ in Hubble's terminology. Northern and southern skies were surveyed for galaxies and tens of thousands were recorded. In 1932 he produced a catalog, with Adelaide Ames, of 1249 galaxies, which included over a thousand galaxies brighter than 13th magnitude. In 1937 he published a survey of 36,000 southern galaxies. He also studied the Magellanic Clouds and identified the first two dwarf galaxies, the Fornax and Sculptor systems, which are members of the Local Group of galaxies.

Shapley wrote several books on astronomy and left an account of his scientific life in his informal Through Rugged Ways to the Stars (1969).

The American astronomer Harlow Shapley (1885-1972) proved that our solar system is only a peripheral member of our galaxy. He is credited with bringing Harvard Observatory into a position of preeminence in the world of astronomy.

Harlow Shapley was born on Nov. 2, 1885, in Nashville, Missouri, where his father was a successful hay producer and dealer. Harlow received his early education in a one-room country schoolhouse. About age 15, he went to a kind of business school in Pittsburg, Kansas, and within a year, became a newspaper reporter. He saved his money and resolved to get educated." He was accepted by the Carthage Collegiate Institute, from which he graduated in 1907 as valedictorian of his class.

Shapley then entered the University of Missouri, intending to study journalism, but, finding no degree program available, took up astronomy - and never put it down. In 1910 he received his bachelor's degree; the following year he completed his master's degree. He received the valuable Thaw fellowship of Princeton University and began studying under H. N. Russell. In 1913 Shapley received his doctoral degree.

Shapley's thesis, a lasting contribution to astronomy, dealt with methods for determining the physical properties - for example, the period of revolution, the orbital inclination, and the mean density - of eclipsing binary (double) stars from their light curves" (their intensity as a function of time). From the outset of his work, however, he had a pressing desire to determine the distances to these stars, and, after a trip of several months to Europe, Shapley went in 1914 to Mt. Wilson Observatory to study stellar distances. He made a giant step forward in his research program when, within a year, he realized that the variable Cepheid stars are not eclipsing binaries but single pulsating stars. Their distances, therefore, could be determined by measuring their apparent magnitudes, using Henrietta S. Leavitt's 1912 period-luminosity relationship to obtain their absolute magnitudes, and employing the inverse-square law. Furthermore, since pulsating Cepheid stars frequently occur in the so-called globular clusters, Shapley could employ the former to determine distances to the latter.

Using Mt. Wilson's 60-inch reflecting telescope, Shapley took numerous photographs from 1916 to 1917. Analyzing them, he discovered that although the globular clusters are symmetrically distributed about the plane of the Milky Way, most appear to be concentrated in the direction of the constellation Sagittarius. From these observations, Shapley drew the revolutionary conclusion that our solar system is not at the center of our galaxy but is actually far (roughly 50,000 light-years) off-center. Thus Shapley in 1917 displaced the sun from the center of our galaxy. Moreover, Shapley concluded that our galaxy, lens-shaped, is of immense dimensions: 300,000 light-years in diameter and 30,000 light-years thick. (These estimates had to be revised later to take account both of interstellar absorption and W. Baade's work.)

This revolutionary discovery stimulated protracted debate and was undoubtedly Shapley's greatest single achievement. But his contributions to astronomy by no means stopped in 1917. Four years later he became director of Harvard Observatory and for more than three decades thereafter, simultaneously carried out creative research and fulfilled his administrative duties. He became known as Mr. Magellanic Clouds" for his many studies on this pair of relatively close-by, irregularly shaped galaxies; he discovered in 1938 the first of the dwarf sculptor-type galaxies; he directed immense surveys of stellar spectra and galactic populations - all this, and much more, while bringing the overall research and instructional programs of Harvard Observatory to a position of preeminence in the world.

In addition to being elected to the National Academy of Sciences in 1924, Shapley received numerous honorary degrees, medals, and other high honors. In 1952 he became director emeritus and Paine Professor of Astronomy at Harvard, and in 1956 professor emeritus. He died in 1972.

Further Reading

A selected bibliography is included in Shapley's delightfully written reminiscences, Through Rugged Ways to the Stars (1969). A chapter on his life and work is in Navin Sullivan, Pioneers in Astronomy (1964). For more general background see Sir William C. Dampier, A History of Science (1943); Bernard Jaffe, Men of Science in America (1944); and Willy Ley, Watchers of the Skies (1963).

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