Mount Wilson Observatory - 100 Inch (2.5 M) Hooker Telescope

100 Inch (2.5 M) Hooker Telescope

Once the 60 inch telescope project was well underway, Hale immediately set about creating a larger telescope. John D. Hooker provided crucial funding for it, along with Carnegie. The Saint-Gobain factory was again chosen to cast a blank in 1906, which it completed in 1908, After considerable trouble over the blank (and potential replacements), the 100 inches (2.5 m) telescope was completed and saw "first light" on November 2, 1917. The blank started with over two tons of fused glass which was melted in a furnace into one piece. The blank once melted into one piece took over a year to cool without cracking. As with the 60 inch telescope, the entire telescope is suspended on a mercury bearing, to allow it to turn smoothly.

In 1919 the Hooker telescope was equipped with a special attachment, an optical astronomical interferometer developed by Albert Michelson, much larger than the one he had used to measure Jupiter's satellites. Michelson was able to use the equipment to determine the precise diameter of stars, such as Betelgeuse, the first time the size of a star had ever been measured. Henry Norris Russell developed his star classification system based on observations using the Hooker.

In 1935 the silver coating used since 1917 on the Hooker 100 inch mirror was replaced with a more modern and longer lasting aluminum metallic coating that reflected 50% more light than the older silver method of coating. The newer method of coating for the telescope mirrors was first tested on the older 60 inch mirror telescope.

Edwin Hubble performed his critical calculations from work on the 100 inches (2.5 m) telescope. He determined that some nebulae were actually galaxies outside our own Milky Way. Hubble, assisted by Milton L. Humason, discovered the presence of the redshift that indicated the universe is expanding.

The Hooker's reign of three decades as the largest telescope came to an end when the Caltech-Carnegie consortium completed its 200-inch (5.1 m) telescope in 1948 at Palomar Observatory, 90 miles (140 km) south, in San Diego County, California.

By the 1980s, the focus of astronomy research had turned to deep space observation, which required darker skies than what could be found in the Los Angeles area, due to ever-increasing problem of light pollution. In 1986, the Carnegie Institution, which ran the observatory, handed it over to the non-profit Mount Wilson Institute. At that time, the 100 inches (2.5 m) telescope was deactivated, but it was restarted in 1992 and outfitted with adaptive optics. The Hooker telescope remains one of the pre-eminent scientific instruments of the 20th century.

The telescope has a resolving power of 0.05 arcsecond.