Mount Wilson Observatory

Mount Wilson Observatory

Overview

The Mount Wilson Observatory (MWO) is an astronomical observatory in Los Angeles County, California
Los Angeles County, California
Los Angeles County is a county in the U.S. state of California. As of 2010 U.S. Census, the county had a population of 9,818,605, making it the most populous county in the United States. Los Angeles County alone is more populous than 42 individual U.S. states...

, United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...

. The MWO is located on Mount Wilson
Mount Wilson (California)
Mount Wilson is one of the better known peaks in the San Gabriel Mountains, part of the Angeles National Forest in Los Angeles County, California. It is the location of the Mount Wilson Observatory and has become the astronomical center of Southern California with and telescopes, and and tall...

, a 5,715 foot (1,742 m) peak in the San Gabriel Mountains
San Gabriel Mountains
The San Gabriel Mountains Range is located in northern Los Angeles County and western San Bernardino County, California, United States. The mountain range lies between the Los Angeles Basin and the Mojave Desert, with Interstate 5 to the west and Interstate 15 to the east...

 near Pasadena
Pasadena, California
Pasadena is a city in Los Angeles County, California, United States. Although famous for hosting the annual Rose Bowl football game and Tournament of Roses Parade, Pasadena is the home to many scientific and cultural institutions, including the California Institute of Technology , the Jet...

, northeast of Los Angeles
Los Ángeles
Los Ángeles is the capital of the province of Biobío, in the commune of the same name, in Region VIII , in the center-south of Chile. It is located between the Laja and Biobío rivers. The population is 123,445 inhabitants...

. The observatory contains two historically important telescopes: the 60 inch (1.5 m) Hale telescope built in 1908, and the 100 inch (2.5 m) Hooker telescope, which was the largest telescope in the world from its completion in 1917 until 1948.

Thanks to the inversion layer
Inversion (meteorology)
In meteorology, an inversion is a deviation from the normal change of an atmospheric property with altitude. It almost always refers to a temperature inversion, i.e...

 that traps smog
Smog
Smog is a type of air pollution; the word "smog" is a portmanteau of smoke and fog. Modern smog is a type of air pollution derived from vehicular emission from internal combustion engines and industrial fumes that react in the atmosphere with sunlight to form secondary pollutants that also combine...

 over Los Angeles, Mount Wilson has naturally steadier air than any other location in North America, making it ideal for astronomy
Astronomy
Astronomy is a natural science that deals with the study of celestial objects and phenomena that originate outside the atmosphere of Earth...

 and in particular for interferometry
Interferometry
Interferometry refers to a family of techniques in which electromagnetic waves are superimposed in order to extract information about the waves. An instrument used to interfere waves is called an interferometer. Interferometry is an important investigative technique in the fields of astronomy,...

.
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Encyclopedia

The Mount Wilson Observatory (MWO) is an astronomical observatory in Los Angeles County, California
Los Angeles County, California
Los Angeles County is a county in the U.S. state of California. As of 2010 U.S. Census, the county had a population of 9,818,605, making it the most populous county in the United States. Los Angeles County alone is more populous than 42 individual U.S. states...

, United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...

. The MWO is located on Mount Wilson
Mount Wilson (California)
Mount Wilson is one of the better known peaks in the San Gabriel Mountains, part of the Angeles National Forest in Los Angeles County, California. It is the location of the Mount Wilson Observatory and has become the astronomical center of Southern California with and telescopes, and and tall...

, a 5,715 foot (1,742 m) peak in the San Gabriel Mountains
San Gabriel Mountains
The San Gabriel Mountains Range is located in northern Los Angeles County and western San Bernardino County, California, United States. The mountain range lies between the Los Angeles Basin and the Mojave Desert, with Interstate 5 to the west and Interstate 15 to the east...

 near Pasadena
Pasadena, California
Pasadena is a city in Los Angeles County, California, United States. Although famous for hosting the annual Rose Bowl football game and Tournament of Roses Parade, Pasadena is the home to many scientific and cultural institutions, including the California Institute of Technology , the Jet...

, northeast of Los Angeles
Los Ángeles
Los Ángeles is the capital of the province of Biobío, in the commune of the same name, in Region VIII , in the center-south of Chile. It is located between the Laja and Biobío rivers. The population is 123,445 inhabitants...

. The observatory contains two historically important telescopes: the 60 inch (1.5 m) Hale telescope built in 1908, and the 100 inch (2.5 m) Hooker telescope, which was the largest telescope in the world from its completion in 1917 until 1948.

Thanks to the inversion layer
Inversion (meteorology)
In meteorology, an inversion is a deviation from the normal change of an atmospheric property with altitude. It almost always refers to a temperature inversion, i.e...

 that traps smog
Smog
Smog is a type of air pollution; the word "smog" is a portmanteau of smoke and fog. Modern smog is a type of air pollution derived from vehicular emission from internal combustion engines and industrial fumes that react in the atmosphere with sunlight to form secondary pollutants that also combine...

 over Los Angeles, Mount Wilson has naturally steadier air than any other location in North America, making it ideal for astronomy
Astronomy
Astronomy is a natural science that deals with the study of celestial objects and phenomena that originate outside the atmosphere of Earth...

 and in particular for interferometry
Interferometry
Interferometry refers to a family of techniques in which electromagnetic waves are superimposed in order to extract information about the waves. An instrument used to interfere waves is called an interferometer. Interferometry is an important investigative technique in the fields of astronomy,...

. The increasing light pollution
Light pollution
Light pollution, also known as photopollution or luminous pollution, is excessive or obtrusive artificial light.The International Dark-Sky Association defines light pollution as:...

 due to the growth of greater Los Angeles
Greater Los Angeles Area
The Greater Los Angeles Area, or the Southland, is a term used for the Combined Statistical Area sprawled over five counties in the southern part of California, namely Los Angeles County, Orange County, San Bernardino County, Riverside County and Ventura County...

 has limited the ability of the observatory to engage in deep space astronomy, but it remains a productive center, with many new and old instruments in use for astronomical research.

The observatory was conceived and founded by 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...

, who had built the 40 inch (1 m) telescope at the Yerkes Observatory
Yerkes Observatory
Yerkes Observatory is an astronomical observatory operated by the University of Chicago in Williams Bay, Wisconsin. The observatory, which calls itself "the birthplace of modern astrophysics," was founded in 1897 by George Ellery Hale and financed by Charles T. Yerkes...

. The Mount Wilson Solar Observatory was first funded by the Carnegie Institution of Washington in 1904, leasing the land from the owners of the Mount Wilson Hotel in 1904. Among the conditions of the lease was that it allow public access.

60 inch (1.5 m) Telescope



George Ellery Hale received the 60 inch (1.5 m) mirror blank, cast by Saint-Gobain
Saint-Gobain
Saint-Gobain S.A. is a French multinational corporation, founded in 1665 in Paris and headquartered on the outskirts of Paris at La Défense and in Courbevoie. Originally a mirror manufacturer, it now also produces a variety of construction and high-performance materials.The company has its head...

 in France, in 1896 as a gift from his father, William Hale. It was a glass disk 7½ inches (191 mm) thick and weighing 1900 pounds (860 kg). However it was not until 1904 that Hale received funding from the Carnegie Institution to build an observatory. Grinding began in 1905 and took two years. The mounting and structure for the telescope was built in San Francisco and barely survived the 1906 earthquake
1906 San Francisco earthquake
The San Francisco earthquake of 1906 was a major earthquake that struck San Francisco, California, and the coast of Northern California at 5:12 a.m. on Wednesday, April 18, 1906. The most widely accepted estimate for the magnitude of the earthquake is a moment magnitude of 7.9; however, other...

. Transporting the pieces to the top of Mount Wilson was an enormous task. "First light" was December 8, 1908. It was at the time the largest operational telescope in the world.

The 60 inch reflector became one of the most productive and successful telescopes in astronomical history. Its design and light-gathering power allowed the pioneering of spectroscopic analysis, parallax
Parallax
Parallax is a displacement or difference in the apparent position of an object viewed along two different lines of sight, and is measured by the angle or semi-angle of inclination between those two lines. The term is derived from the Greek παράλλαξις , meaning "alteration"...

 measurements, nebula
Nebula
A nebula is an interstellar cloud of dust, hydrogen gas, helium gas and other ionized gases...

 photography, and photometric
Photometry (astronomy)
Photometry is a technique of astronomy concerned with measuring the flux, or intensity of an astronomical object's electromagnetic radiation...

 photography. Though surpassed in size by the Hooker telescope nine years later, the Hale telescope remained one of the largest in use for decades.

In 1992, the 60 inch telescope was fitted with an early 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, the Atmospheric Compensation Experiment (ACE). The 69-channel system improved the potential resolving power of the telescope from 0.5-1.0 arc sec to 0.07 arc sec. ACE was developed by DARPA for the Strategic Defense Initiative
Strategic Defense Initiative
The Strategic Defense Initiative was proposed by U.S. President Ronald Reagan on March 23, 1983 to use ground and space-based systems to protect the United States from attack by strategic nuclear ballistic missiles. The initiative focused on strategic defense rather than the prior strategic...

 system, and the National Science Foundation
National Science Foundation
The National Science Foundation is a United States government agency that supports fundamental research and education in all the non-medical fields of science and engineering. Its medical counterpart is the National Institutes of Health...

 funded the civilian conversion.

Today, the 60 inch telescope is used for public outreach. Eyepieces are fitted to its focus instead of instruments. It is the largest telescope in the world devoted to the general public. As of June 2009, the cost for a half-night of observation is $900, $1700 for a full night.

100 inch (2.5 m) Hooker Telescope



Hale immediately set about creating a larger telescope. John D. Hooker provided crucial funding for it, along with 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...

. The Saint-Gobain factory was again chosen to cast a blank in 1906, which it completed in 1908, After considerable trouble over the blank (and potential replacements), the 100 inch (2.5 m) telescope was completed and saw "first light" on November 2, 1917. The blank started with over two tons of fused glass which was melted in a furnace into one piece. The blank once melted into one piece took over a year to cool without cracking.

Just like the 60" telescope, the mechanism incorporates a mercury float to provide smooth operation. The Hooker telescope was equipped in 1919 with a special attachment, an optical astronomical interferometer
Astronomical interferometer
An astronomical interferometer is an array of telescopes or mirror segments acting together to probe structures with higher resolution by means of interferometry....

 developed by Albert Michelson, much larger than the one he had used to measure Jupiter's satellites. Michelson was able to use the equipment to determine the precise diameter of stars, such as Betelgeuse
Betelgeuse
Betelgeuse, also known by its Bayer designation Alpha Orionis , is the eighth brightest star in the night sky and second brightest star in the constellation of Orion, outshining its neighbour Rigel only rarely...

, the first time the size of a star had ever been measured. Henry Norris Russell
Henry Norris Russell
Henry Norris Russell was an American astronomer who, along with Ejnar Hertzsprung, developed the Hertzsprung–Russell diagram . In 1923, working with Frederick Saunders, he developed Russell–Saunders coupling which is also known as LS coupling.-Biography:Russell was born in 1877 in Oyster Bay, New...

 developed his star classification system based on observations using the Hooker.

In 1935 the silver coating used since 1917 on the Hooker 100 inch mirror was replaced with a more modern and longer lasting aluminum metallic coating that reflected 50% more light than the older silver method of coating. The newer method of coating for the telescope mirrors was first tested on the older 60 inch mirror telescope.


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...

 performed his critical calculations from work on the 100 inch (2.5 m) telescope. He determined that some nebulae were actually galaxies
Galaxy
A galaxy is a massive, gravitationally bound system that consists of stars and stellar remnants, an interstellar medium of gas and dust, and an important but poorly understood component tentatively dubbed dark matter. The word galaxy is derived from the Greek galaxias , literally "milky", a...

 outside our own Milky Way
Milky Way
The Milky Way is the galaxy that contains the Solar System. This name derives from its appearance as a dim un-resolved "milky" glowing band arching across the night sky...

. Hubble, assisted by Milton L. Humason
Milton L. Humason
Milton Lasell Humason was an American astronomer. He was born in Dodge Center, Minnesota.He dropped out of school and had no formal education past the age of 14. Because he loved the mountains, and Mount Wilson in particular, he became a "mule skinner" taking materials and equipment up the...

, discovered the presence of the redshift
Redshift
In physics , redshift happens when light seen coming from an object is proportionally increased in wavelength, or shifted to the red end of the spectrum...

 that indicated the universe is expanding.

The Hooker's reign of three decades as the largest telescope came to an end when the Caltech-Carnegie consortium completed its 200 inches (5.1 m) 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...

 in 1948 at 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...

, 90 miles (150 km) south, 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...

.

By the 1980s, the focus of astronomy research had turned to deep space observation, which required darker skies than what could be found in the Los Angeles area, due to ever-increasing problem of light pollution
Light pollution
Light pollution, also known as photopollution or luminous pollution, is excessive or obtrusive artificial light.The International Dark-Sky Association defines light pollution as:...

. In 1986, the Carnegie Institution, which ran the observatory, handed it over to the non-profit Mount Wilson Institute. At that time, the 100 inch (2.5 m) telescope was deactivated, but it was restarted in 1992 and outfitted with adaptive optics. The Hooker telescope remains one of the pre-eminent scientific instruments of the 20th century.

The telescope has a resolving power of 0.05 arcsecond
Minute of arc
A minute of arc, arcminute, or minute of angle , is a unit of angular measurement equal to one sixtieth of one degree. In turn, a second of arc or arcsecond is one sixtieth of one minute of arc....

.

Solar telescopes


There are three solar telescopes, two of which are now used for astronomical research, also known as solar tower
Solar tower
A solar tower, in the context of astronomy, is a structure used to support equipment for studying the sun, and is typically part of solar telescope designs. Generically, the term solar tower has many more uses especially for a type of power production using Earth's Sun...

s due to their construction. The 60 foot (18 m) tower telescope was completed in 1908, and the 150 foot (46 m) tower telescope was completed in 1912. The Snow solar telescope, built in 1904 is used for educational demonstrations. The telescopes are used to study helioseismology
Helioseismology
Helioseismology is the study of the propagation of wave oscillations, particularly acoustic pressure waves, in the Sun. Unlike seismic waves on Earth, solar waves have practically no shear component . Solar pressure waves are believed to be generated by the turbulence in the convection zone near...

 and other changes in the sun
Sun
The Sun is the star at the center of the Solar System. It is almost perfectly spherical and consists of hot plasma interwoven with magnetic fields...

's nature.

Interferometry


The extremely steady air over Mount Wilson is well suited to interferometry, the use of multiple viewing points to increase resolution enough to allow for the direct measurement of the size of details such as star diameters. Michelson
Albert Abraham Michelson
Albert Abraham Michelson was an American physicist known for his work on the measurement of the speed of light and especially for the Michelson-Morley experiment. In 1907 he received the Nobel Prize in Physics...

 performed the first measurements of other stars in the history of astronomical interferometry on the Hooker telescope in 1919.

The Infrared Spatial Interferometer
Infrared Spatial Interferometer
The Infrared Spatial Interferometer is an astronomical interferometer array of three 65 inch telescopes operating in the mid-infrared. The telescopes are fully mobile and their current site on Mount Wilson allows for placements as far as 70 m apart, giving the resolution of a telescope of that...

 (ISI) is an array of three 65 inch (1.65 m) telescopes operating in the mid-infrared. The telescopes are fully mobile and their current site on Mount Wilson allows for placements as far as 70 m apart, giving the resolution of a telescope of that diameter. The signals are converted to radio frequencies through heterodyne
Heterodyne
Heterodyning is a radio signal processing technique invented in 1901 by Canadian inventor-engineer Reginald Fessenden where high frequency signals are converted to lower frequencies by combining two frequencies. Heterodyning is useful for frequency shifting information of interest into a useful...

 circuits and then combined electronically using techniques copied from radio astronomy
Radio astronomy
Radio astronomy is a subfield of astronomy that studies celestial objects at radio frequencies. The initial detection of radio waves from an astronomical object was made in the 1930s, when Karl Jansky observed radiation coming from the Milky Way. Subsequent observations have identified a number of...

. ISI is run by an arm of the University of California, Berkeley
University of California, Berkeley
The University of California, Berkeley , is a teaching and research university established in 1868 and located in Berkeley, California, USA...

. The longest (70m) baseline provides a resolution of 0.003 arcsec at 11 micrometers. On July 9, 2003, ISI recorded the first closure phase
Closure phase
The closure phase is an observable quantity in imaging astronomical interferometry, which allowed the use of interferometry with very long baselines. It forms the basis of the self-calibration approach to interferometric imaging...

 aperture synthesis
Aperture synthesis
Aperture synthesis or synthesis imaging is a type of interferometry that mixes signals from a collection of telescopes to produce images having the same angular resolution as an instrument the size of the entire collection...

 measurements in the mid infrared.

The Center for High Angular Resolution Astronomy (CHARA) array
CHARA array
The CHARA Array is an optical astronomical interferometer operated by The Center for High Angular Resolution Astronomy of the Georgia State University . CHARA is the World's highest angular resolution telescope at near-infrared wavelengths...

 is an interferometer formed from six 1 m (40-inch) telescopes arranged along three axes with a maximum separation length of 330 m. The light beams travel through vacuum tubes and are combined optically, requiring a building 100 meters long with movable mirrors to keep the light in phase as the earth rotates. CHARA is operated by the Georgia State University
Georgia State University
Georgia State University is a research university in downtown Atlanta, Georgia, USA. Founded in 1913, it serves about 30,000 students and is one of the University System of Georgia's four research universities...

 and began scientific use in 2002 and began "routine operations" in early 2004. In infrared the integrated image can resolve down to 0.0005 arcseconds. As of 2005, four of the six telescopes have been commissioned for interferometric observations.

These and other astronomical interferometers are included in the List of astronomical interferometers at visible and infrared wavelengths. The history of the development of these instruments is given in History of astronomical interferometry.

Other telescopes


A 24 inches (609.6 mm) telescope fitted with an infrared detector purchased from a military contractor was used by Eric Becklin
Eric Becklin
Eric E. Becklin is an American astrophysicist, best known for his pioneering study of infra-red sources at the center of our galaxy....

 in 1966 to determine the center of the Milky Way
Milky Way
The Milky Way is the galaxy that contains the Solar System. This name derives from its appearance as a dim un-resolved "milky" glowing band arching across the night sky...

 for the first time.

In 1968, the first large-area near-IR (2.2 µm) survey of the sky was conducted by Gerry Neugebauer and Robert B. Leighton using a 62 inches (1.6 m) reflecting dish they had built. The instrument is now in the Smithsonian.

History

  • Letters to the Mount Wilson Observatory are the subject of a permanent exhibition at the Museum of Jurassic Technology
    Museum of Jurassic Technology
    The Museum of Jurassic Technology is an educational institution dedicated to the advancement of knowledge and the public appreciation of the lower jurassic...

     in Los Angeles, California
    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...

    . A small room is dedicated to a collection of unusual letters and theories received by the observatory circa 1915–1935. These letters were also collected in the book No One May Ever Have the Same Knowledge Again: Letters to Mt. Wilson Observatory 1915–1935 (ISBN 0-9647215-0-3).
  • The historic monument came under threat during the August 2009 California wildfires.
  • The poet Alfred Noyes
    Alfred Noyes
    Alfred Noyes was an English poet, best known for his ballads, "The Highwayman" and "The Barrel-Organ".-Early years:...

     was present for the "first light" of the Hooker telescope on November 2, 1917. Noyes used this night as the setting in the opening of Watchers of the Sky, the first volume in his trilogy The Torchbearers, an epic poem about the history of science. According to his account of the night, the first object viewed in the telescope was Jupiter and Noyes himself was the first to see one of the planet's moons through the telescope.

See also


External links