Index: History; Instruments; Sources.
Discovered the variation in the periods of Cepheid stars which became the standard for the “Period-Luminosity Law”.
Henrietta Leavitt made a very important discovery using photographic plates taken by the Metcalf 10-inch refractor. She has never been to South Africa (to my knowledge). The Metcalf telescope used is now housed at Boyden Observatory, Bloemfontein. Due to the connection between her and the telescope she is mentioned here.
The Magellanic Clouds. What are they? Superficially they look like broken-off parts of the Milky Way, but they were obviously of great importance and at Arequipa (first Boyden Observatory in Peru), many photographs of them were taken with the Metcalf 10-inch refractor. The plates were sent back to Harvard for analysis and a member of the staff, Miss Henrietta Leavitt, began to study them. She was particularly interested in the Cepheids, of which there were plenty to be found.
Miss Leavitt concentrated on the Cepheids in the Small Cloud of Magellan and made a surprising discovery. Due to her work, the “Period-Luminosity Law” was established & she discovered the standard candle (light intensity) to be used to measure distances. “… she could measure the periods of the Cepheids by comparing plates taken on different nights; and she found that the Cepheids with longer periods were always brighter than Cepheids with shorter periods. There was a definite relationship, and the significance of it could hardly be over-emphasised, because to all intents and purposes the Cepheids in the Small Cloud were at the same distance from us, just as for most practical purposes it may be said that Johannesburg and Pretoria are the same distance from New York. Therefore, if the Cloud Cepheids were equally distant, then those, which looked the brighter, must actually be the brighter. It followed that the real luminosity of a Cepheid could be found merely by measuring its period of variation. Because the Cepheids in the Cloud are no different from Cepheids anywhere else, it became possible to measure relative distances“. [Copied from Moore, p.127.]
“Shapley, at Harvard, was quick to take advantage of this “Period-Luminosity Law”. He studied the Cepheids in the great assemblages of stars known as globular clusters, which lie around the edges of our Galaxy; he measured the distances of the Cepheids, and hence the distances of the globulars; and he was able to draw up the first reliable scale-map of the Galaxy. Later, in 1923, Edwin Hubble at Mount Wilson, in California, studied the Cepheids in spiral nebulae, and was able to prove that these remarkable objects are independent galaxies, far beyond our own. Since then the Cepheids have played a vital role in all studies of the distribution and distances of stars and galaxies. Inevitably there have been complications; for instance there was an error in the basic Cepheid scale which did not emerge until the 1950s, and in a famous paper delivered to an enthralled audience in London the late Walter Baade doubled the size of the universe “at a stroke”. But everything depended upon the Period-Luminosity Law, and it was the Metcalf telescope which took the essential photographs.” [Copied from Moore, p.127.]
Henrietta Leavitt reduced photographic plates taken with the Metcalf telescope.
Sources: – Leavitt
Moore, P. & Collins, P., Astronomy in Southern Africa, p.127. (General Source)