Harlow Shapley

Harlow Shapley was an American astronomer who used globular clusters to estimate the Milky Way’s size and showed that the Sun lies far from its center.

Great Debate: The 1920 debate between Harlow Shapley and Heber Curtis over the scale of the universe and the nature of spiral nebulae. Shapley’s model of a vast Milky Way framed one side of this dispute.
Globular cluster: A dense, roughly spherical collection of old stars bound together by gravity. Shapley mapped these clusters to infer the Milky Way’s size and center.
Heber Curtis: An American astronomer who argued that spiral nebulae were separate galaxies and that the Milky Way was relatively small. Curtis opposed Shapley’s large-Galaxy model during the 1920 debate.
Mount Wilson Observatory: An astronomical observatory in California that housed some of the early twentieth century’s largest telescopes. Shapley used its telescopes to study globular clusters and variable stars.
Milky Way: The barred spiral galaxy containing the Solar System and billions of other stars. Shapley’s work transformed estimates of this galaxy’s dimensions and structure.
Cepheid variable: A pulsating star whose period of brightness variation is related to its intrinsic luminosity. Cepheids in globular clusters supplied distance estimates for Shapley’s map.
Henrietta Swan Leavitt: An American astronomer who discovered the period-luminosity relation for Cepheid variable stars. Her discovery supplied the calibration that made Shapley’s stellar distance estimates possible.
Harvard College Observatory: A Harvard astronomical research institution founded in 1839 and known for extensive stellar observations. Shapley conducted much of his research there and later directed it.
Galactic Center: The central region of the Milky Way, roughly 26,000 light-years from the Sun. His distance measurements placed the Sun well away from this center.
Leavitt's law: The relation between a Cepheid variable’s pulsation period and its intrinsic luminosity. It enabled Cepheids to serve as distance indicators in the cluster measurements.

Linked from 14 pages