13 Jul Discovering Mount Wilson Chapter 5: First Light
Chapter five of ‘Discovering Mount Wilson’ brings us to the 60-inch telescope. Under direction of Observatory founder George Ellery Hale, it was completed in 1908 and was the world’s largest operational telescope until he went on to finish the Mount Wilson 100-inch telescope in 1917.
Hale received the 60-inch mirror blank in 1896 while still at Yerkes Observatory as a gift from his father. Funding for the 60-inch telescope came from the Carnegie Institution of Washington in 1904 and once in place, Hale was finally able to start the process of building the 60-telescope. Grinding of the mirror blank began in 1905 and took two years to complete. The finished parabolic mirror is 7⅝ inches thick at the edge, 6⅞ inches thick in the center, and weighs 1,900 pounds. The shape of the mirror had to be perfect to within a few millionths of an inch across its five-foot surface. To ensure accuracy, a special room was built, the windows were made with double glass and sealed tight. Anyone entering the room had to wear a surgical gown and cap to prevent foreign materials interfering with the grinding process.
The mounting and structure for the telescope were built in San Francisco and barely survived the 1906 earthquake. Transporting the pieces to the top of Mount Wilson was an enormous task. More than 150 tons of material for the building and 60-inch telescope dome was pulled to the top by mule teams. One truck was reserved for the heaviest pieces of the mounting, the most difficult of which was the telescope tube, 6 1/2 feet wide and 18 feet long, which was transported as a single piece.
With all of the pieces in place, the heart of the telescope, the 60-inch mirror, was mounted in the telescope on December 7, 1908. A few evenings later on December 13, the telescope was used for the first time, and the first photographs from it were taken on December 24.
For 85 years, the 60-inch telescope had been in use almost every clear night, becoming one of the most successful and productive telescopes in history.