The Hooker 100-inch telescope is named after John D. Hooker, who provided the funds for the giant mirror. It was the largest telescope in the world from 1917 to 1948 when the 200-inch telescope was built on Palomar Mountain 90 miles to the southeast. Many great discoveries were made with the 100-inch telescope Edwin Hubble's refinement of the distance scale of the universe. The first optical interferometer ever used for astronomical research was used on the 100-inch telescope to measure the sizes of distant stars for the first time in 1919.
The 100-inch telescope has three optical configurations available to meet the requirements of a wide variety research projects. A very high-resolution spectrograph is located at the telescope's Coudé focus. Located on the ground floor of the 100-inch telescope dome, the Aluminizing Room is used to recoat all of the telescope mirrors at the observatory. Operating the large telescope sometimes also means having to do some very strange jobs!
The 100-inch telescope was inactive from 1986 to 1994. It subsequently underwent major upgrades to its control systems and is once again used for scientific research, although great care was taken to preserve elements of its history. A state-of-the-art adaptive optics system has been created for the 100-inch. This and other important additions to the telescope keep the 100-inch well prepared for research in the 21st century.
A camera mounted near the top of the 150-foot solar tower telescope shows various views around the observatory including the 100-inch telescope (camera and service courtesy of the UCLA group at the 150-foot tower).