Hale’s Four Great Telescopes

The Observatory’s founder, George Ellery Hale, built four telescopes, each one in succession becoming the largest in the world. His first was the 40-inch refractor at Yerkes  (in Wisconsin) on the left, but then he began building the more revolutionary–and more compact–reflector telescopes, using a large glass mirror instead of a lens. His next two are on Mount Wilson, the 60-inch and the 100-inch–both responsible for profound changes in our understanding of the Universe. His fourth, the 200-inch Hale Telescope at Palomar is represented on the right by one of Russell Porter’s famous cutaway drawings which has been extended on the left to show the relative size of the full dome. Hale’s telescopes were the most powerful from 1897, when Yerkes opened, to 1993, when the Keck telescope in Hawaii was completed, surpassing Palomar’s light gathering power–a span of 96 years! The one challenge to this impressive span came in 1978, when the Soviet Union fixed their 236-inch (6 meter) telescope, the BTA-6, with a new mirror. But even then, it was plagued with many problems, including a less than ideal location in the Caucasus Mountains with fog on 50% of the nights and relatively poor seeing on the rest. Photo credits: University of Chicago/Yerkes Observatory, Carnegie Observatories, Palomar Observatory/Caltech.

The Next Big Thing

On tours of Mount Wilson, after seeing two telescopes that were once the biggest in the world, the question often arises: Which one is the current light-gathering champion? To answer that question it is helpful to look at a graphic comparing the size of past big telescopes, like those that Hale built, with current heavy hitters, and those that are either under construction or planned. The next big telescope will be the Giant Magellan, now well under way in Chile, under direction of Carnegie Observatories which built Mount Wilson’s telescopes. But it is interesting to note that currently the telescope system with the highest resolution (but not light-gathering power)  is back on Mount Wilson: the CHARA Array synthesizes a mirror nearly a fifth of a mile across and can discern features on distant stars.

The staff at Carnegie Observatories, who are leading the effort to build the Giant Magellan Telescope in Chile, pose for a group shot in their parking lot in Pasadena. The large white circles represent the size of the seven 8.4 meter mirrors that will go into the next big telescope. Photo credit: Carnegie Institution of Washington.