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| Alternative names | Palomar 5.1m Hale |
|---|---|
| Part of | Palomar Observatory[1] |
| Location(s) | California, Pacific States Region |
| Coordinates | 33°21′23″N116°51′54″W / 33.35628°N 116.86489°W /33.35628; -116.86489 |
| Altitude | 1,713 m (5,620 ft) |
| First light | January 26, 1949, 10:06 pmPST |
| Discovered | Caliban,Sycorax,Jupiter LI,Alcor B |
| Diameter | 200 in (5.1 m) |
| Collecting area | 31,000 sq in (20 m2) |
| Focal length | 16.76 m (55 ft 0 in) |
| Website | www |
  Location of Hale Telescope | |
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TheHale Telescope is a 200-inch (5.1 m),f/3.3reflecting telescope at thePalomar Observatory inSan Diego County,California, US, named after astronomerGeorge Ellery Hale. With funding from theRockefeller 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-largesttelescope, and pioneered many new technologies intelescope mount design and in the design and fabrication of its large aluminum coated "honeycomb" lowthermal expansionPyrex mirror.[2] It was completed in 1949 and is still in active use.
The Hale Telescope represented the technological limit in building large optical telescopes for over 30 years. It was thelargest telescope in the world from its construction in 1949 until theSovietBTA-6 was built in 1976, and the second largest until the construction of theKeck Observatory Keck 1 inHawaii in 1993.
Hale supervised the building of the telescopes at theMount Wilson Observatory with grants from theCarnegie Institution of Washington: the 60-inch (1.5 m) telescope in 1908 and the 100-inch (2.5 m) telescope in 1917. These telescopes were very successful, leading to the rapid advance in understanding of the scale of theUniverse through the 1920s, and demonstrating to visionaries like Hale the need for even larger collectors.[citation needed]
The chief optical designer for Hale's previous 100-inch telescope wasGeorge Willis Ritchey, who intended the new telescope to be ofRitchey–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 parabolicprimary mirror.[3]
In 1928 Hale secured a grant of $6 million from theRockefeller Foundation for "the construction of an observatory, including a 200-inch reflecting telescope" to be administered by theCalifornia Institute of Technology (Caltech), of which Hale was a founding member. In the early 1930s, Hale selected a site at 1,700 m (5,600 ft) onPalomar Mountain inSan Diego County, California, US, as the best site, and less likely to be affected by the growing light pollution problem in urban centers likeLos Angeles. TheCorning Glass Works was assigned the task of making a 200-inch (5.1 m) primary mirror. Construction of the observatory facilities and dome started in 1936, but because of interruptions caused byWorld War II, the telescope was not completed until 1948 when it was dedicated.[4] Due to slight distortions of images, corrections were made to the telescope throughout 1949. It became available for research in 1950.[4]
Postage Stamp. The US Post Office issued a 3c postage stamp in 1948 commemorating the Hale Telescope and Observatory.
A functioning one-tenth scale model of the telescope was also made at Corning.[5]
The 200-inch (510 cm) telescope sawfirst light on January 26, 1949, at 10:06 pmPST[6][7] under the direction of American astronomerEdwin Powell Hubble, targetingNGC 2261, an object also known as Hubble's Variable Nebula.[8][9]
The telescope continues to be used every clear night for scientific research by astronomers from Caltech and their operating partners,Cornell University, theUniversity of California, and theJet Propulsion Laboratory. It is equipped with modern optical and infrared array imagers, spectrographs, and anadaptive optics[10] system. It has also usedlucky cam imaging, which in combination with adaptive optics pushed the mirror close to itstheoretical resolution for certain types of viewing.[10]
One of the Corning Labs' glass test blanks for the Hale was used for theC. Donald Shane telescope's 120-inch (300 cm) primary mirror.[11]
The collecting area of the mirror is about 31,000 square inches (20 square meters).[12]
The Hale Telescope uses a special type ofequatorial mount called a "horseshoe mount", a modified yoke mount that replaces the polar bearing with an open "horseshoe" structure that gives the telescope full access to the entire sky, includingPolaris and stars near it. The optical tube assembly (OTA) uses aSerrurier truss, then newly invented byMark U. Serrurier of Caltech in Pasadena in 1935, designed to flex in such a way as to keep all of the optics in alignment.[13]
Originally, the Hale Telescope was going to use a primary mirror of fused quartz manufactured by General Electric,[14] but instead the primary mirror was cast in 1934 atCorning Glass Works in New York state using Corning's then new material calledPyrex (borosilicate glass).[15]
The mirror was cast in a mold with 36 raised mold blocks (similar in shape to awaffle iron). This created ahoneycomb mirror that cut the amount of Pyrex needed down from over 40 short tons (36 t) to just 20 short tons (18 t), making a mirror that would cool faster in use and have multiple "mounting points" on the back to evenly distribute its weight (note – see external links 1934 article for drawings).[16] The shape of a central hole was also part of the mold so light could pass through the finished mirror when it was used in aCassegrain configuration (a Pyrex plug for this hole was also made to be used during the grinding and polishing process[17]). While the glass was being poured into the mold during the first attempt to cast the 200-inch mirror, the intense heat caused several of the molding blocks to break loose and float to the top, ruining the mirror. The defective mirror was used to test the annealing process. After the mold was re-engineered, a second mirror was successfully cast.[citation needed]
After cooling several months, the finished mirror blank was transported by rail to Pasadena, California.[18][19] Once in Pasadena the mirror was transferred from the rail flat car to a specially designed semi-trailer for road transport to where it would be polished.[20] In the optical shop in Pasadena (now the Synchrotron building at Caltech) standard telescopemirror making techniques were used to turn the flat blank into a precise concave parabolic shape, although they had to be executed on a grand scale. A special 240 in (6.1 m) 25,000 lb (11 t)mirror cell jig was constructed which could employ five different motions when the mirror was ground and polished.[21] Over 13 years almost 10,000 lb (4.5 t) of glass was ground and polished away, reducing the weight of the mirror to 14.5 short tons (13.2 t). The mirror was coated (and still is re-coated every 18–24 months) with a reflective aluminum surface using the same aluminum vacuum-deposition process invented in 1930 by Caltech physicist and astronomerJohn Strong.[22]
The Hale's 200 in (510 cm) mirror was near the technological limit of a primary mirror made of a single rigid piece of glass.[23][24] Using a monolithic mirror much larger than the 5-meter Hale or 6-meter BTA-6 is prohibitively expensive due to the cost of both the mirror, and the massive structure needed to support it. A mirror beyond that size would also sag slightly under its own weight as the telescope is rotated to different positions,[25][26] changing the precision shape of the surface, which must be accurate to within 2 millionths of an inch (50nm). Modern telescopes over 9 meters use a different mirror design to solve this problem, with either a single thin flexible mirror or a cluster of smallersegmented mirrors, whose shape is continuously adjusted by a computer-controlledactive optics system using actuators built into themirror support cell.[citation needed]
The moving weight of the upper dome is about 1000 US tons, and can rotate on wheels.[27] The dome doors weigh 125 tons each.[28] The dome is made of welded steel plates about 10 mm thick.[27]
The first observation of the Hale Telescope was ofNGC 2261 on January 26, 1949.[29]
During its first 50 years, the Hale Telescope made many significant contributions to stellar evolution, cosmology, and high-energy astrophysics.[30] Similarly, the telescope, and the technology developed for it, advanced the study of the spectra of stars, interstellar matter, AGNs, and quasars.[31]
Quasars were first identified as high redshift sources by spectra taken with the Hale Telescope.[32]
Halley's Comet (1P) upcoming 1986 approach to the Sun was first detected by astronomersDavid C. Jewitt and G. Edward Danielson on 16 October 1982 using the 200-inch Hale Telescope equipped with aCCD camera.[33]
Two moons of the planetUranus were discovered in September 1997, bringing the planet's total known moons to 17 at that time.[34] One wasCaliban (S/1997 U 1), which was discovered on 6 September 1997 byBrett J. Gladman,Philip D. Nicholson,Joseph A. Burns, andJohn J. Kavelaars using the 200-inch Hale Telescope.[35] The other Uranian moon discovered then isSycorax (initial designation S/1997 U 2) and was also discovered using the 200 inch Hale Telescope.[36]
TheCornell Mid-Infrared Asteroid Spectroscopy (MIDAS) survey used the Hale Telescope with a spectrograph to study spectra from 29 asteroids.[37]
In 2009, using a coronograph, the Hale Telescope was used to discover the starAlcor B, which is a companion to Alcor in theBig Dipper.[38]
In 2010, a new satellite of planetJupiter was discovered with the 200-inch Hale, called S/2010 J 1 and later namedJupiter LI.[39]
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 color.[40][41]
In December 2023 the Hale Telescope began serving as the receiving antenna for theDeep Space Optical Communications experiment on NASA'sPsyche mission.[42]
Up until the year 2010,telescopes could onlydirectly image exoplanets under exceptional circumstances. Specifically, it is easier to obtain images when the planet is especially large (considerably larger thanJupiter), widely separated from its parent star, and hot so that it emits intense infrared radiation. However, in 2010 a team fromNASA'sJet Propulsion Laboratory demonstrated that avortex coronagraph could enable small scopes to directly image planets.[43]
The Hale had four times the light-collecting area of the second-largest scope when it was commissioned in 1949. Other contemporary telescopes were theHooker Telescope at the Mount Wilson Observatory and theOtto Struve Telescope at the McDonald Observatory.[citation needed]
| # | Name / Observatory | Image | Aperture | Altitude | First Light | Special advocate(s) |
|---|---|---|---|---|---|---|
| 1 | Hale Telescope Palomar Obs. |  | 200-inch 508 cm | 1713 m (5620 ft) | 1949 | George Ellery Hale John D. Rockefeller Edwin Hubble |
| 2 | Hooker Telescope[44] Mount Wilson Obs. |  | 100-inch 254 cm | 1742 m (5715 ft) | 1917 | George Ellery Hale Andrew Carnegie |
| 3 | McDonald Obs. 82-inch[45] McDonald Observatory (i.e. Otto Struve Telescope) |  | 82-inch 210 cm | 2070 m (6791 ft) | 1939 | Otto Struve |
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