What was the name of the 100-inch telescope on Mount Wilson that Hubble used?

The 100-inch telescope on Mount Wilson that Edwin Hubble used was the Hooker Telescope. Completed in 1917, it was then the world's largest telescope and became one of the most influential instruments in astronomical history.

Hubble used it to identify Cepheid variable stars in the Andromeda Nebula during the early 1920s. Because Cepheids have a reliable relationship between their pulsation period and true brightness, they act as distance indicators. Hubble's measurements showed that Andromeda lay far beyond the Milky Way and was actually a separate galaxy.

The telescope also helped Hubble and Milton Humason measure galaxy redshifts and establish the relationship between distance and apparent recession speed associated with the expanding universe. A common mix-up is the Hale Telescope: it was the later 200-inch instrument at Palomar Observatory, not the 100-inch telescope on Mount Wilson.