The Hale Telescope is a 5.1 m, f/3.3 reflecting telescope at the Palomar Observatory in San Diego County, California named after astronomer George Ellery Hale.
With funding from the Rockefeller Foundation in 1928, he orchestrated the planning, design, and construction of the observatory, but with the project ending up taking 20 years he did not live to see its commissioning.
The Hale was groundbreaking for its time, with double the diameter of the second-largest telescope, and pioneered many new technologies in telescope mount design and in the design and fabrication of its large aluminium coated honeycomb low thermal expansion Pyrex mirror. It was completed in 1949 and is still in active use.
More information: Palomar Observatory
The Hale Telescope represented the technological limit in building large optical telescopes for over 30 years.
It was the largest telescope in the world from its construction in 1949 until the Soviet BTA-6 was built in 1976, and the second largest until the construction of the Keck Observatory Keck 1 in Hawaii in 1993.
Hale supervised the building of the telescopes at the Mount Wilson Observatory with grants from the Carnegie Institution of Washington: the 1.5 m telescope in 1908 and the 2.5 m telescope in 1917. These telescopes were very successful, leading to the rapid advance in understanding of the scale of the Universe through the 1920s, and demonstrating to visionaries like Hale the need for even larger collectors.
The chief optical designer for Hale's previous telescope was George Willis Ritchey, who intended the new telescope to be of Ritchey–Chrétien design. Compared to the usual parabolic primary, this design would have provided sharper images over a larger usable field of view. However, Ritchey and Hale had a falling-out. With the project already late and over budget, Hale refused to adopt the new design, with its complex curvatures, and Ritchey left the project. The Mount Palomar Hale Telescope turned out to be the last world-leading telescope to have a parabolic primary mirror.
In the early 1930s, Hale selected a site at 1,700 m on Palomar Mountain in San Diego County, California, as the best site, and less likely to be affected by the growing light pollution problem in urban centres like Los Angeles.
The Corning Glass Works was assigned the task of making a 5.1 m primary mirror. Construction of the observatory facilities and dome started in 1936, but because of interruptions caused by World War II, the telescope was not completed until 1948 when it was dedicated. Due to slight distortions of images, corrections were made to the telescope throughout 1949. It became available for research in 1950.
A functioning one tenth scale model of the telescope was also made at Corning.
The 510 cm telescope saw first light on January 26, 1949, at 10:06 pm PST under the direction of American astronomer Edwin Powell Hubble, targeting NGC 2261, an object also known as Hubble's Variable Nebula. The photographs made then were published in the astronomical literature and in the May 7, 1949 issue of Collier's Magazine.
The telescope continues to be used every clear night for scientific research by astronomers from Caltech and their operating partners, Cornell University, the University of California, and the Jet Propulsion Laboratory. It is equipped with modern optical and infrared array imagers, spectrographs, and an adaptive optics system. It has also used lucky cam imaging, which in combination with adaptive optics pushed the mirror close to its theoretical resolution for certain types of viewing.
One of the Corning Labs' glass test blanks for the Hale was used for the C. Donald Shane telescope's 300 cm primary mirror. The collecting area of the mirror is about 20 square meters.
More information: Space
The first observation of the Hale telescope was of NGC 2261 on January 26, 1949.
Halley's Comet (1P) upcoming 1986 approach to the Sun was first detected by astronomers David C. Jewitt and G. Edward Danielson on 16 October 1982 using the Hale telescope equipped with a CCD camera.
Two moons of the planet Uranus were discovered in September 1997, bringing the planet's total known moons to 17 at that time. One was Caliban (S/1997 U 1), which was discovered on 6 September 1997 by Brett J. Gladman, Philip D. Nicholson, Joseph A. Burns, and John J. Kavelaars using the Hale telescope. The other Uranian moon discovered then is Sycorax (initial designation S/1997 U 2) and was also discovered using the Hale telescope.
In 1999, astronomers used a near-infrared camera and adaptive optics to take some of the best Earth-surface based images of planet Neptune up to that time. The images were sharp enough to identify clouds in the ice giant's atmosphere.
The Cornell Mid-Infrared Asteroid Spectroscopy (MIDAS) survey used the Hale Telescope with a spectrograph to study spectra from 29 asteroids. An example of a result from that study, is that the asteroid 3 Juno was determined to have an average radius of 135.7±11 km using the infrared data.
In 2009, using a coronagraph, the Hale Telescope was used to discover the star Alcor B, which is a companion to Alcor in the famous Big Dipper constellation.
In 2010, a new satellite of planet Jupiter was discovered with the Hale Telescope, called S/2010 J 1 and later named Jupiter LI.
In October 2017 the Hale Telescope was able to record the spectrum of the first recognized interstellar object, 1I/2017 U1 ʻOumuamua; while no specific mineral was identified it showed the visitor had a reddish surface colour.
More information: NASA
Like buried treasures,
the outposts of the universe have beckoned
to the adventurous from immemorial times...
George Ellery Hale
