Harlow Shapley

At Mount Wilson from 1914, Shapley used variable-star brightnesses to estimate globular-cluster distances. His 1918 work identified their system’s centre with the Galactic centre, placing the Sun off-centre. Its numerical distance scale was later revised.

References: [1]

Shapley debated Heber Curtis over cosmic scale and spiral nebulae. His work on the Milky Way’s extent was distinct from his view that spiral nebulae belonged within its system; subsequent galaxy-distance observations overturned the latter.

References: [1]

As director from 1921, he organised research on variable stars, the Magellanic Clouds and galaxies, and developed graduate training. Cannon’s classification work and Payne-Gaposchkin’s research continued during his directorship.

References: [1]