Hale telescope
Encyclopedia
F-number
In optics, the f-number of an optical system expresses the diameter of the entrance pupil in terms of the focal length of the lens; in simpler terms, the f-number is the focal length divided by the "effective" aperture diameter...
reflecting telescope
Reflecting telescope
A reflecting telescope is an optical telescope which uses a single or combination of curved mirrors that reflect light and form an image. The reflecting telescope was invented in the 17th century as an alternative to the refracting telescope which, at that time, was a design that suffered from...
at the Palomar Observatory
Palomar Observatory
Palomar Observatory is a privately owned observatory located in San Diego County, California, southeast of Pasadena's Mount Wilson Observatory, in the Palomar Mountain Range. At approximately elevation, it is owned and operated by the California Institute of Technology...
in California
California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...
, named after astronomer George Ellery Hale
George Ellery Hale
George Ellery Hale was an American solar astronomer.-Biography:Hale was born in Chicago, Illinois. He was educated at MIT, at the Observatory of Harvard College, , and at Berlin . As an undergraduate at MIT, he is known for inventing the spectroheliograph, with which he made his discovery of...
. With funding from the Rockefeller Foundation
Rockefeller Foundation
The Rockefeller Foundation is a prominent philanthropic organization and private foundation based at 420 Fifth Avenue, New York City. The preeminent institution established by the six-generation Rockefeller family, it was founded by John D. Rockefeller , along with his son John D. Rockefeller, Jr...
, he orchestrated the planning, design, and construction of the observatory, but did not live to see its commissioning. The Hale was groundbreaking for its time, with double the diameter of the next largest telescope
Telescope
A telescope is an instrument that aids in the observation of remote objects by collecting electromagnetic radiation . The first known practical telescopes were invented in the Netherlands at the beginning of the 1600s , using glass lenses...
and pioneering the use of many technologies such as vapor deposited
Evaporation (deposition)
Evaporation is a common method of thin film deposition. The source material is evaporated in a vacuum. The vacuum allows vapor particles to travel directly to the target object , where they condense back to a solid state...
aluminum and low thermal expansion
Thermal expansion
Thermal expansion is the tendency of matter to change in volume in response to a change in temperature.When a substance is heated, its particles begin moving more and thus usually maintain a greater average separation. Materials which contract with increasing temperature are rare; this effect is...
glass
Glass
Glass is an amorphous solid material. Glasses are typically brittle and optically transparent.The most familiar type of glass, used for centuries in windows and drinking vessels, is soda-lime glass, composed of about 75% silica plus Na2O, CaO, and several minor additives...
.
It was the largest aperture optical telescope in the world from its completion in 1948 until the BTA-6
BTA-6
The BTA-6 is a 6 m aperture optical telescope at the Special Astrophysical Observatory located in the Zelenchuksky District on the north side of the Caucasus Mountains in southern Russia...
was built in 1976, and the second largest until the construction of the Keck 1 in 1993.
History
Mount Wilson Observatory
The Mount Wilson Observatory is an astronomical observatory in Los Angeles County, California, United States. The MWO is located on Mount Wilson, a 5,715 foot peak in the San Gabriel Mountains near Pasadena, northeast of Los Angeles...
with grants from the Carnegie Institution of Washington: the 60 inches (1.5 m) telescope in 1908 and the 100 inches (2.5 m) telescope in 1917. These telescopes were very successful, leading to the rapid advance in understanding of the scale of the Universe
Universe
The Universe is commonly defined as the totality of everything that exists, including all matter and energy, the planets, stars, galaxies, and the contents of intergalactic space. Definitions and usage vary and similar terms include the cosmos, the world and nature...
through the 1920s, and demonstrating to visionaries like Hale the need for even larger collectors.
In 1928 Hale secured a grant of US$
United States dollar
The United States dollar , also referred to as the American dollar, is the official currency of the United States of America. It is divided into 100 smaller units called cents or pennies....
6 million from the Rockefeller Foundation
Rockefeller Foundation
The Rockefeller Foundation is a prominent philanthropic organization and private foundation based at 420 Fifth Avenue, New York City. The preeminent institution established by the six-generation Rockefeller family, it was founded by John D. Rockefeller , along with his son John D. Rockefeller, Jr...
for "the construction of an observatory, including a 200 inches (5.1 m) reflecting telescope" to be administered by the California Institute of Technology
California Institute of Technology
The California Institute of Technology is a private research university located in Pasadena, California, United States. Caltech has six academic divisions with strong emphases on science and engineering...
(Caltech), of which Hale was a founding member. In the early 1930s, Hale selected a site at 1700 m (5,577.4 ft) on Palomar Mountain
Palomar Mountain
Palomar Mountain is a mountain in the Peninsular Ranges in northern San Diego County. It is famous as the location of the Palomar Observatory and Hale Telescope, and known for the Palomar Mountain State Park.-History:...
in San Diego County, California
San Diego County, California
San Diego County is a large county located in the southwestern corner of the US state of California. Hence, San Diego County is also located in the southwestern corner of the 48 contiguous United States. Its county seat and largest city is San Diego. Its population was about 2,813,835 in the 2000...
, USA as the best site, and less likely to be affected by the growing light pollution problem in urban centers like Los Angeles
Los Angeles, California
Los Angeles , with a population at the 2010 United States Census of 3,792,621, is the most populous city in California, USA and the second most populous in the United States, after New York City. It has an area of , and is located in Southern California...
. The Corning Glass Works was assigned the task of making a 200 inches (5.1 m) primary mirror
Primary mirror
A primary mirror is the principal light-gathering surface of a reflecting telescope.-Description:The primary mirror of a reflecting telescope is a spherical or parabolic shaped disks of polished reflective metal , or in later telescopes, glass or other material coated with a reflective layer...
. Construction of the observatory facilities and dome started in 1936, but because of interruptions caused by World War II
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...
, 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.
The 200 inches (508 cm) Hale saw first light on January 26, 1949 under the direction of American astronomer Edwin Powell Hubble, targeting NGC 2261
NGC 2261
NGC 2261 is a variable nebula located in the constellation Monoceros. It is illuminated by the star R Monocerotis , which is not directly visible itself....
, 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
Cornell University
Cornell University is an Ivy League university located in Ithaca, New York, United States. It is a private land-grant university, receiving annual funding from the State of New York for certain educational missions...
, the University of California
University of California
The University of California is a public university system in the U.S. state of California. Under the California Master Plan for Higher Education, the University of California is a part of the state's three-tier public higher education system, which also includes the California State University...
, and the Jet Propulsion Laboratory
Jet Propulsion Laboratory
Jet Propulsion Laboratory is a federally funded research and development center and NASA field center located in the San Gabriel Valley area of Los Angeles County, California, United States. The facility is headquartered in the city of Pasadena on the border of La Cañada Flintridge and Pasadena...
. It is equipped with modern optical and infrared array imagers, spectrographs, and an adaptive optics
Adaptive optics
Adaptive optics is a technology used to improve the performance of optical systems by reducing the effect of wavefront distortions. It is used in astronomical telescopes and laser communication systems to remove the effects of atmospheric distortion, and in retinal imaging systems to reduce the...
system. It has also used Lucky cam, which, in combination with adaptive optics pushed the mirror close to its theoretical resolution for certain types of viewing. (see Lucky imaging
Lucky imaging
Lucky imaging is one form of speckle imaging used for astronomical photography. Speckle imaging techniques use a high-speed camera with exposure times short enough so that the changes in the Earth's atmosphere during the exposure are minimal.With lucky imaging, those optimum exposures least...
)
One of the Corning Labs glass test blanks for the Hale was used for the C. Donald Shane telescope
C. Donald Shane telescope
The C. Donald Shane telescope is a reflecting telescope located at the Lick Observatory in California. It was named after astronomer C. Donald Shane in 1978, who led the effort to acquire the necessary funds from the California Legislature, and who then oversaw the telescope's construction...
's 120 inches (304.8 cm) primary mirror.
The collecting area of the Hale is about 31,000 square inches (20 square meters).
200-inch mirror
Originally, the Hale telescope was going to use a large fuzed quartz block manufactured by General Electric , but instead the primary mirror for the Hale telescope was cast in 1934 at Corning Glass Works in New York State using Corning's then new material called PyrexPyrex
Pyrex is a brand name for glassware, introduced by Corning Incorporated in 1915.Originally, Pyrex was made from borosilicate glass. In the 1940s the composition was changed for some products to tempered soda-lime glass, which is the most common form of glass used in glass bakeware in the US and has...
(borosilicate glass
Borosilicate glass
Borosilicate glass is a type of glass with the main glass-forming constituents silica and boron oxide. Borosilicate glasses are known for having very low coefficients of thermal expansion , making them resistant to thermal shock, more so than any other common glass...
). Pyrex was chosen for its low expansion qualities so the large mirror would not distort the images produced when it changed shape due to temperature variations (a problem that plagued earlier large telescopes). The mirror was cast in mold with 36 raised mold blocks (similar in shape to a waffle iron
Waffle iron
A waffle iron is a cooking appliance used to make waffles.It usually consists of two hinged metal plates, molded to create the honeycomb pattern found on waffles...
). This created a honeycomb mirror
Honeycomb mirror
A honeycomb mirror is a large mirror usually used as the primary mirror in astronomical reflecting telescopes whose face is supported by a ribbed structure that resembles a honeycomb. The design provides sufficient rigidity for ultra-high precision optics while reducing the weight of the mirror...
that cut the amount of Pyrex needed down from over 40 tons to just 20 tons, 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) . 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 a Cassegrain
Cassegrain reflector
The Cassegrain reflector is a combination of a primary concave mirror and a secondary convex mirror, often used in optical telescopes and radio antennas....
configuration (a Pyrex plug for this hole was also made to be used during the grinding a polishing process). 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.
After cooling several months, the finished mirror blank was transported by rail to Pasadena, California. Once in Pasadena the mirror was transferred from the rail flat car to a specially designed semi-trail for road transport to where it would be polished. In the optical shop in Pasadena standard telescope mirror 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 inch 25,000 lbs mirror cell jig was constructed which could employ five different motions when the mirror was ground and polished. Over 13 years almost 10,000 pounds of glass was ground and polished away reducing the weight of the mirror to 14.5 tons. 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 astronomer John Strong.
The Hale's 200-inch mirror was near the technological limit of a primary mirror made of a single rigid piece of glass. 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, changing the precision shape of the surface, which must be accurate to within 2 millionths of an inch (25 nm). Modern telescopes over 6 meters use a different mirror design to solve this problem, with either a single thin flexible mirror or a cluster of smaller segmented mirror
Segmented mirror
A segmented mirror is an array of smaller mirrors designed to act as segments of a single large curved mirror. The segments can be either spherical or asymmetric . They are used as objectives for large reflecting telescopes...
s, whose shape is continuously adjusted by a computer-controlled active optics
Active optics
Active optics is a technology used with reflecting telescopes developed in the 1980s, which actively shapes a telescope's mirrors to prevent deformation due to external influences such as wind, temperature, mechanical stress...
system using actuators built into the mirror support cell
Mirror support cell
In astronomy the mirror support cell - more commonly mirror cell - is the component of a reflecting telescope which supports the mirror in place to hold optical alignment, allow collimation adjustment, and protect it from falling out...
.
Mounting structures
The Hale telescope uses a special type of equatorial mountEquatorial mount
An equatorial mount is a mount for instruments that follows the rotation of the sky by having one rotational axis parallel to the Earth's axis of rotation. This type of mount is used for astronomical telescopes and cameras...
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 including Polaris and stars near it. The optical tube assembly (OTA) uses a Serrurier truss
Serrurier truss
A Serrurier truss is used in telescope tube assembly construction. The design was created in 1935 by engineer Mark U. Serrurier when he was working on the Mt. Palomar Hale telescope. The design solves the problem of truss flexing by supporting the primary objective mirror and the secondary mirror...
, then newly invented by Mark U. Serrurier of Caltech in Pasadena in 1935, designed to flex in such a way as to keep all of the optics in alignment.
Contemporaries on commissioning
The Palomar Hale had four times the light collecting area than the next largest scope when it came online.Three largest telescopes in 1949:
| # | Name / Observatory |
Image | Aperture | Altitude | First Light |
Special advocate(s) |
|---|---|---|---|---|---|---|
| 1 | Hale Telescope Hale telescope The Hale Telescope is a , 3.3 reflecting telescope at the Palomar Observatory in California, named after astronomer George Ellery Hale. With funding from the Rockefeller Foundation, he orchestrated the planning, design, and construction of the observatory, but did not live to see its commissioning... Palomar Obs. Palomar Observatory Palomar Observatory is a privately owned observatory located in San Diego County, California, southeast of Pasadena's Mount Wilson Observatory, in the Palomar Mountain Range. At approximately elevation, it is owned and operated by the California Institute of Technology... |
|
200 inch 508 cm |
1713 m (5620 ft) |
1949 | George Ellery Hale George Ellery Hale George Ellery Hale was an American solar astronomer.-Biography:Hale was born in Chicago, Illinois. He was educated at MIT, at the Observatory of Harvard College, , and at Berlin . As an undergraduate at MIT, he is known for inventing the spectroheliograph, with which he made his discovery of... John D. Rockefeller John D. Rockefeller John Davison Rockefeller was an American oil industrialist, investor, and philanthropist. He was the founder of the Standard Oil Company, which dominated the oil industry and was the first great U.S. business trust. Rockefeller revolutionized the petroleum industry and defined the structure of... Edwin Hubble Edwin Hubble Edwin Powell Hubble was an American astronomer who profoundly changed the understanding of the universe by confirming the existence of galaxies other than the Milky Way - our own galaxy... |
| 2 | Hooker Telescope Mount Wilson Obs. Mount Wilson Observatory The Mount Wilson Observatory is an astronomical observatory in Los Angeles County, California, United States. The MWO is located on Mount Wilson, a 5,715 foot peak in the San Gabriel Mountains near Pasadena, northeast of Los Angeles... |
 |
100 inch 254 cm |
1742 m (5715 ft) |
1917 | George Ellery Hale George Ellery Hale George Ellery Hale was an American solar astronomer.-Biography:Hale was born in Chicago, Illinois. He was educated at MIT, at the Observatory of Harvard College, , and at Berlin . As an undergraduate at MIT, he is known for inventing the spectroheliograph, with which he made his discovery of... Andrew Carnegie Andrew Carnegie Andrew Carnegie was a Scottish-American industrialist, businessman, and entrepreneur who led the enormous expansion of the American steel industry in the late 19th century... |
| 3 | Otto Struve Telescope Otto Struve Telescope The Otto Struve Telescope was the first major telescope to be built at McDonald Observatory. Located in the Davis Mountains in West Texas, the Otto Struve Telescope was designed by Warner & Swasey Company and constructed between 1933 and 1939 by the Paterson-Leitch Company. Its 2.1 meter mirror... McDonald Obs. McDonald Observatory The McDonald Observatory is an astronomical observatory located near the unincorporated community of Fort Davis in Jeff Davis County, Texas, United States. The facility is located on Mount Fowlkes and Mount Locke in the Davis Mountains of West Texas... |
 |
82 inch 210 cm |
2070 m (6791 ft) |
1939 | Otto Struve Otto Struve Otto Struve was a Russian astronomer. In Russian, his name is sometimes given as Otto Lyudvigovich Struve ; however, he spent most of his life and his entire scientific career in the United States... |
Direct imaging of exoplanets
Up until the year 2010, telescopes could only directly image exoplanets under exceptional circumstances. Specifically, it is easier to obtain images when the planet is especially large (considerably larger than JupiterJupiter
Jupiter is the fifth planet from the Sun and the largest planet within the Solar System. It is a gas giant with mass one-thousandth that of the Sun but is two and a half times the mass of all the other planets in our Solar System combined. Jupiter is classified as a gas giant along with Saturn,...
), widely separated from its parent star, and hot so that it emits intense infrared radiation. However in 2010 a team from NASA
NASA
The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...
s Jet Propulsion Laboratory
Jet Propulsion Laboratory
Jet Propulsion Laboratory is a federally funded research and development center and NASA field center located in the San Gabriel Valley area of Los Angeles County, California, United States. The facility is headquartered in the city of Pasadena on the border of La Cañada Flintridge and Pasadena...
demonstrated that a vortex coronagraph
Coronagraph
A coronagraph is a telescopic attachment designed to block out the direct light from a star so that nearby objects – which otherwise would be hidden in the star's bright glare – can be resolved...
could enable small scopes to directly image planets. They did this by imaging the previously imaged HR 8799
HR 8799
HR 8799 is a young main sequence star located 129 light years away from Earth in the constellation of Pegasus, with roughly 1.5 times the Sun's mass and 4.9 times its luminosity. It is part of a system that also contains a debris disk and at least four massive planets...
planets using just a 1.5 m portion of the Hale Telescope
Hale telescope
The Hale Telescope is a , 3.3 reflecting telescope at the Palomar Observatory in California, named after astronomer George Ellery Hale. With funding from the Rockefeller Foundation, he orchestrated the planning, design, and construction of the observatory, but did not live to see its commissioning...
.
See also
- Serrurier trussSerrurier trussA Serrurier truss is used in telescope tube assembly construction. The design was created in 1935 by engineer Mark U. Serrurier when he was working on the Mt. Palomar Hale telescope. The design solves the problem of truss flexing by supporting the primary objective mirror and the secondary mirror...
- List of largest optical reflecting telescopes
- List of largest optical telescopes historically
- List of largest optical telescopes in the 20th century
Further reading
- Building the 200-inch telescope ASIN: B00088GJH2
- The Perfect Machine: Building the Palomar Telescope ISBN 9780060926700
- Explorations With the Hale Telescope ASIN: B000Q9Z28A
- The possibilities of large telescopes ASIN: B0008CUW94
- Dedication of the Hale telescope ASIN: B0007FFYR2
- First Light: The Search for the Edge of the UniverseFirst Light (Preston book)First Light: The Search for the Edge of the Universe is a 1987 non-fiction book on astronomy and astronomers by Richard Preston.The title refers to the astronomical term first light, which is when a telescope is first used to take an astronomical image after it has been constructed...
ISBN 9780871132000 - The function of large telescopes ASIN: B0008B1JTW
- THE 200-INCH HALE TELESCOPE AND SOME PROBLEMS IT MAY SOLVE ASIN: B000P6HRW8
External links
- "Giant New Telescope" June 1934, Popular Science Monthly – ie one of the first detailed article on the Hale telescope and construction of its 200 inch mirror
- The 200 inches (5,080 mm) Hale Telescope
- Palomar Skies: Palomar History Photo of the Week