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Shapley, Harlow

galaxy centre distances light

(1885–1972) US astronomer: discovered structure of our Galaxy.

The son of a farmer, Shapley was a teenage crime reporter on two newspapers before entering the University of Missouri, intending to study journalism; he soon changed to astronomy. In 1915, using ‘Cepheid variable’ method of estimating stellar distances, Shapley was able to provide the first reasonable picture of the structure and size of our own Galaxy. He studied the distribution of globular star clusters, by means of the Cepheids within them, and showed that they are concentrated disproportionately in the direction of Sagittarius. This, he argued, must be the centre of our disc-shaped Galaxy, and in 1920 he estimated the Sun to be about 50 000 light years from the galactic centre. The overall diameter of our Galaxy (the Milky Way) he believed to be about 300 000 light years (both figures have since been shown to be overestimates). However, he underestimated the distances of some spiral nebulae, and better values were got later by . Shapley directed the Hale Observatory at Harvard from 1921–52.

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