* Astronomy

Blobrana · L

RE: William Wilson Morgan (1906 – 1994)

Blobrana · L

William Wilson Morgan (January 3, 1906 - June 21, 1994) was an American astronomer.

The principal theme in Morgan's work was the study of stellar and galaxy classification. Along with Philip Keenan he developed the MK system for the classification of stars through their spectra. He also developed several galaxy morphological classification systems, including the first systems to use the physical properties of galaxies, as opposed to simple eye-ball estimates favoured by Edwin Hubble. He invented the now widely used classification cD for massive galaxies in the centres of clusters.
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Blobrana · L

Title: W. W. Morgan and the Discovery of the Spiral Arm Structure of our Galaxy
Authors: William Sheehan

William Wilson Morgan was one of the great astronomers of the twentieth century. He considered himself a morphologist, and was preoccupied throughout his career with matters of classification. Though his early life was difficult, and his pursuit of astronomy as a career was opposed by his father, he took a position at Yerkes Observatory in 1926 and remained there for the rest of his working life. Thematically, his work was also a unified whole. Beginning with spectroscopic studies under Otto Struve at Yerkes Observatory, by the late 1930s he concentrated particularly on the young O and B stars. His work on stellar classification led to the Morgan-Keenan- Kellman [MKK] system of classification of stars, and later - as he grappled with the question of the intrinsic colour and brightness of stars at great distances - to the Johnson-Morgan UBV system for measuring stellar colours. Eventually these concerns with classification and method led to his greatest single achievement - the recognition of the nearby spiral arms of our Galaxy by tracing the OB associations and HII regions that outline them. After years of intensive work on the problem of galactic structure, the discovery came in a blinding flash of Archimedean insight as he walked under the night sky between his office and his house in the autumn of 1951. His optical discovery of the spiral arms preceded the radio-mapping of the spiral arms by more than a year. Morgan suffered a nervous breakdown soon after he announced his discovery, however, and so was prevented from publishing a complete account of his work. As a result of that, and the announcement soon afterward of the first radio maps of the spiral arms, the uniqueness of his achievement was not fully appreciated at the time.

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