Caption: The 100 inch (2.54 m) Hooker telescope at Mount Wilson Observatory near Los Angeles, California. It is the telescope that Edwin Hubble (1889--1953) used to discover that galaxies were galaxies in 1924 (see Wikipedia: Edwin Hubble: Universe goes beyond the Milky Way galaxy) and to discover the general expansion of the universe and Hubble's law in and he may not have been sure earlier. 1929 (see Wikipedia: Edwin Hubble: Redshift increases with distance; Wikipedia: Expansion of the universe: History). When this photograph was taken in 1989, the Hooker telescope had just been mothballed. It was re-activated later for research, but since 2014, it has been used for visual astronomy for public outreach.

By the by, the Hooker telescope was the largest telescope (i.e., had the largest primary mirror/lens and, therefore, the most light-gathering power) from first light in 1916 until 200 inch (5.08 m) Hale telescope was completed in 1949 at Palomar Observatory, San Diego County, California.

Essential to Hubble's discoveries was the fact that he had access to the largest telescope of his day in Southern California which is intrinsically one of the world's best observing sites. Air pollution and light pollution have greatly diminished Southern California's observing qualities.

Before the Hooker telescope, the largest telescope was the Leviathan of Parsonstown (1.83 m, operational 1845--c.1890). Before the Leviathan, the largest telescope was William Herschel's (1738--1822) 1.26-m telescope (1789--1840) which was a bit too large for Herschel to use easily.

All these giant telescope's were reflector telescopes: i.e., they used concave mirrors as a primaries. Herschel's 1.26-m telescope and the Leviathan for the primary used speculum, an alloy of copper and tin with a dash of arsenic---which gives that je ne sais quoi---invented for reflector telescope mirrors by Isaac Newton (1643--1727). Speculum is brittle, tarnishes easily, and reflects only about 16 % of incident light.

The Hooker telescope and Hale telescope have glass primaries (for high rigidity) and have reflective coatings of aluminum (Al). Before sometime in 1935, the Hooker telescope used a silver (Ag) (see Wikipedia: Mount Wilson Observatory: 100-inch Hooker telescope).

Credit/Permission: © Andrew Dunn (AKA User:Solipsist), 1989 / Creative Commons CC BY-SA 2.0.
Image link: Wikipedia: File:100inchHooker.jpg.
Local file: local link: hooker.
File: Telescope file: telescope_hooker.html.