Palomar Observatory

Last updated
Palomar Observatory
P200 Dome Open.jpg
Organization California Institute of Technology   Blue pencil.svg
Observatory code 261, 644, 675   Blue pencil.svg
Location San Diego County, California
Coordinates 33°21′23″N116°51′54″W / 33.3564°N 116.865°W / 33.3564; -116.865 Coordinates: 33°21′23″N116°51′54″W / 33.3564°N 116.865°W / 33.3564; -116.865
Altitude1,712 m (5,617 ft) Blue pencil.svg
Established1928  Blue pencil.svg
Website Blue pencil.svg
Telescopes18-inch Schmidt camera
Hale Telescope
Palomar Testbed Interferometer
Samuel Oschin telescope   Blue pencil.svg
Usa edcp relief location map.png
Red pog.svg
Location of Palomar Observatory
Commons-logo.svg Related media on Wikimedia Commons

Palomar Observatory is an astronomical observatory located in San Diego County, California, United States, 145 kilometers (90 mi) southeast of Los Angeles, California, in the Palomar Mountain Range. It is owned and operated by the California Institute of Technology (Caltech) located in Pasadena, California. Research time is granted to Caltech and its research partners, which include the Jet Propulsion Laboratory (JPL) and Cornell University. [1]

Observatory location used for observing terrestrial or celestial events

An observatory is a location used for observing terrestrial or celestial events. Astronomy, climatology/meteorology, geophysical, oceanography and volcanology are examples of disciplines for which observatories have been constructed. Historically, observatories were as simple as containing an astronomical sextant or Stonehenge.

San Diego County, California County in California, United States

San Diego County, officially the County of San Diego, is a county in the southwestern corner of the state of California, in the United States. As of the 2010 census, the population was 3,095,313. making it California's second-most populous county and the fifth-most populous in the United States. Its county seat is San Diego, the eighth-most populous city in the United States. It is the southwesternmost county in the 48 contiguous United States.

Los Angeles City in California

Los Angeles, officially the City of Los Angeles and often known by its initials L.A., is the most populous city in California, the second most populous city in the United States, after New York City, and the third most populous city in North America. With an estimated population of four million, Los Angeles is the cultural, financial, and commercial center of Southern California. The city is known for its Mediterranean climate, ethnic diversity, Hollywood and the entertainment industry, and its sprawling metropolis. Los Angeles is the largest city on the West Coast of North America.


The observatory operates several telescopes, including the 200-inch (5.1 m) Hale Telescope and the 48-inch (1.2 m) Samuel Oschin Telescope. In addition, other instruments and projects have been hosted at the observatory, such as the Palomar Testbed Interferometer and the historic 18-inch (0.46 m) Schmidt telescope, Palomar Observatory's first telescope, dating from 1936.

Hale Telescope Telescope at Palomar Observatory in California, USA

The Hale Telescope is a 200-inch (5.1 m), f/3.3 reflecting telescope at the Palomar Observatory in California, US, 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 aluminum coated "honeycomb" low thermal expansion Pyrex mirror. It was completed in 1948 and is still in active use.

Palomar Testbed Interferometer long-baseline interferometer at the American Palomar Observatory in San Diego County, California, US

The Palomar Testbed Interferometer (PTI) was a near infrared, long-baseline stellar interferometer located at Palomar Observatory in north San Diego County, California, United States. It was built by Caltech and the Jet Propulsion Laboratory and was intended to serve as a testbed for developing interferometric techniques to be used at the Keck Interferometer. It began operations in 1995 and achieved routine operations in 1998, producing more than 50 refereed papers in a variety of scientific journals covering topics from high precision astrometry to stellar masses, stellar diameters and shapes. PTI concluded operations in 2008 and has since been dismantled.


Hale's vision for large telescopes and Palomar Observatory

Astronomer George Ellery Hale, whose vision created the Palomar Observatory, built the world's largest telescope four times. He published an article that was to become the 200-inch Palomar reflector; it was an invitation to the American public to learn about how large telescopes could help answer questions relating to the fundamental nature of the universe. Hale hoped that the American people would understand and support his project even though the country was in the depths of the Great Depression.

George Ellery Hale American solar astronomer

George Ellery Hale was an American solar astronomer, best known for his discovery of magnetic fields in sunspots, and as the leader or key figure in the planning or construction of several world-leading telescopes; namely, the 40-inch refracting telescope at Yerkes Observatory, 60-inch Hale reflecting telescope at Mount Wilson Observatory, 100-inch Hooker reflecting telescope at Mount Wilson, and the 200-inch Hale reflecting telescope at Palomar Observatory. He also played a key role in the foundation of the International Union for Cooperation in Solar Research and the National Research Council, and in developing the California Institute of Technology into a leading research university.

Hale followed this article with a letter to the International Education Board (later absorbed into the General Education Board) of the Rockefeller Foundation dated April 16, 1928 in which he requested funding for this project. In his letter, Hale stated:

The General Education Board was a philanthropy which was used primarily to support higher education and medical schools in the United States, and to help rural white and black schools in the South, as well as modernize farming practices in the South. It helped eradicate hookworm and created the county agent system in American agriculture, linking research as state agricultural experiment stations with actual practices in the field.

The Rockefeller Foundation is a private foundation based at 420 Fifth Avenue, New York City. It was established by the six-generation Rockefeller family. The Foundation was started by Standard Oil owner John D. Rockefeller ("Senior"), along with his son John D. Rockefeller Jr. ("Junior"), and Senior's principal oil and gas business and philanthropic advisor, Frederick Taylor Gates, in New York State on May 14, 1913, when its charter was formally accepted by the New York State Legislature. Its stated mission is "promoting the well-being of humanity throughout the world."

"No method of advancing science is so productive as the development of new and more powerful instruments and methods of research. A larger telescope would not only furnish the necessary gain in light space-penetration and photographic resolving power, but permit the application of ideas and devices derived chiefly from the recent fundamental advances in physics and chemistry."

Hale Telescope

The 200-inch telescope is named after astronomer and project manager George Hale. It was built by Caltech with a $6 million grant from the Rockefeller Foundation, using a Pyrex blank manufactured by Corning Glass Works under the direction of George McCauley after several years of unsuccessful attempts by General Electric under Dr. A.L. Ellis. The first steps toward funding the construction of the 200 inch telescope were taken by Hale in 1928 and included a 23-ton glass block cast by José Antonio de Artigas Sanz. Dr. J.A. Anderson was the initial project manager assigned in the early 1940s. [2] The telescope (the largest in the world at that time) saw first light January 26, 1949 targeting NGC 2261. [3] The American astronomer Edwin Powell Hubble was the first astronomer to use the telescope.

Pyrex trademark for borosilicate glass

Pyrex is a brand introduced by Corning Inc. in 1915 for a line of clear, low-thermal-expansion borosilicate glass used for laboratory glassware and kitchenware. It was later expanded to include clear and opal ware products made of soda-lime glass.

General Electric American industrial company

General Electric Company (GE) is an American multinational conglomerate incorporated in New York City and headquartered in Boston. As of 2018, the company operates through the following segments: aviation, healthcare, power, renewable energy, digital industry, additive manufacturing, venture capital and finance, lighting, and oil and gas.

José Antonio de Artigas Sanz was a Spanish engineer who contributed to the standardization of terminology in the field of electrical engineering.

The 200-inch telescope was the largest telescope in the world from 1949 until 1975, when the Russian BTA-6 telescope saw first light. Astronomers using the Hale Telescope have discovered distant objects at the edges of the known universe called quasars and have given us the first direct evidence of stars in distant galaxies. They have studied the structure and chemistry of intergalactic clouds, leading to an understanding of the synthesis of elements in the universe, and have discovered thousands of asteroids. A one-tenth-scale engineering model of the telescope at Corning Community College in Corning, New York, home of the Corning Glass Works (now Corning Incorporated) was used to discover at least one minor planet, 34419 Corning.

BTA-6 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

The BTA-6 is a 6-metre (20 ft) aperture optical telescope at the Special Astrophysical Observatory located in the Zelenchuksky District on the north side of the Caucasus Mountains in southern Russia.

First light (astronomy) term in astronomy for the first time a telescope is used to look at the Universe

In astronomy, first light is the first use of a telescope to take an astronomical image after it has been constructed. This is often not the first viewing using the telescope; optical tests will probably have been performed in daylight to adjust the components. The first light image is normally of little scientific interest and is of poor quality, since the various telescope elements are yet to be adjusted for optimum efficiency. Despite this, a first light is always a moment of great excitement, both for the people who design and build the telescope and for the astronomical community, who may have anticipated the moment for many years while the telescope was under construction. A well-known and spectacular astronomical object is usually chosen as a subject.

Quasar active galactic nuclei containing a massive black hole

A quasar is an extremely luminous active galactic nucleus (AGN). It has been theorized that most large galaxies contain a supermassive central black hole with mass ranging from millions to billions of times the mass of the Sun. In quasars and other types of AGN, the black hole is surrounded by a gaseous accretion disk. As gas falls toward the black hole, energy is released in the form of electromagnetic radiation, which can be observed across the electromagnetic spectrum. The power radiated by quasars is enormous: the most powerful quasars have luminosities thousands of times greater than a galaxy such as the Milky Way.

Architecture and design

Hale Telescope Dome Palomar Observatory Dome - High Resolution.jpg
Hale Telescope Dome

According to the Observatory's Public Affairs Office, Russell W. Porter was primarily responsible for the Art Deco architecture of the Observatory's buildings, including the dome of the 200-inch Hale Telescope. Porter was also responsible for much of the technical design of the Hale Telescope and Schmidt Cameras, producing a series of cross-section engineering drawings. Porter worked on the designs in collaboration with many engineers and Caltech committee members.[ citation needed ]

Max Mason directed the construction and Theodore von Karman was involved in the engineering.


Palomar Observatory and light pollution

Much of the surrounding region of Southern California has adopted shielded lighting to reduce the light pollution that would potentially affect the observatory. [4]

Telescopes and instruments

Astronomer Jean Mueller posing with the Samuel Oschin Telescope (Schmidt Camera) P48 1994 Jean Large.jpg
Astronomer Jean Mueller posing with the Samuel Oschin Telescope (Schmidt Camera)

Former instruments


The observatory has completed several astronomical surveys: the first in the 1950s, the second in the 1980s and 1990s, and a third in 2003.


The initial Palomar Observatory Sky Survey (POSS or POSS-I), sponsored by the National Geographic institute, was completed in 1958. The first plates were shot in November 1948 and the last in April 1958. This survey was performed using 14 inch2 (6 degree 2) or blue-sensitive (Kodak 103a-O) and red-sensitive (Kodak 103a-E) photographic plates on the 48-inch Samuel Oschin Schmidt reflecting telescope. The survey covered the sky from a declination of +90 degrees (celestial north pole) to −27 degrees and all right ascensions and had a sensitivity to +22 magnitudes (about 1 million times fainter than the limit of human vision). A southern extension extending the sky coverage of the POSS to −33 degrees declination was shot in 1957 – 1958. The final POSS I consisted of 937 plate pairs.

Fritz Zwicky was the first astronomer to observe on Mt. Palomar and was the father of the Sky Survey Technique. [12]

Digitized Sky Survey (DSS) produced images which were based on the photographic data developed in the course of POSS-I. [13]

J.B. Whiteoak, an Australian radio astronomer, used the same instrument to broaden this POSS-I data further. Whiteoaks observations extended south to about −45 degrees declination, using the same field centers as the corresponding northern declination zones. Unlike POSS-I, the Whiteoak extension consisted only of red-sensitive (Kodak 103a-E) photographic plates.


The Second Palomar Observatory Sky Survey (POSS II, sometimes Second Palomar Sky Survey) was performed in the 1980s and 1990s that made use of better, faster films and an upgraded telescope. The Oschin Schmidt was given an achromatic corrector and provisions for autoguiding. Images were recorded in three wavelengths: blue (IIIaJ), red (IIIaF) and near infrared (IVN) plates, respectively. Observers on POSS II included C. Brewer, D. Griffiths, W. McKinley, J. Dave Mendenhall, K. Rykoski, Jeffrey L. Phinney and Jean Mueller (who discovered over 100 supernovae by comparing the POSS I and POSS II plates). Mueller also discovered several comets and minor planets during the course of POSS II and the bright Comet Wilson 1986 was discovered by then graduate student C. Wilson early in the survey. [14]

Until the completion of the Two Micron All Sky Survey (2MASS), POSS II was the most extensive wide-field sky survey ever. When completed, the Sloan Digital Sky Survey will surpass POSS I and POSS II in depth, although the POSS covers almost 2.5 times more area on the sky.

POSS II also exists in digitized form (i.e., the photographic plates were scanned), both in photographic form as the Digitized Sky Survey (DSS) [15] [ clarification needed ]


The multi-year POSS projects were followed by the Palomar Quasar Equatorial Survey Team (QUEST) Variability survey. [16] This survey yielded results that were used by several projects, including the Near-Earth Asteroid Tracking project. Another program that used the QUEST results discovered 90377 Sedna on 14 November 2003, and around 40 Kuiper belt objects. Other programs that share the camera are Shri Kulkarni's search for gamma-ray bursts (this takes advantage of the automated telescope's ability to react as soon as a burst is seen and take a series of snapshots of the fading burst), Richard Ellis' search for supernovae to test whether the universe's expansion is accelerating or not, and S. George Djorgovski's quasar search.

The camera for the Palomar QUEST Survey was a mosaic of 112 Charge-coupled devices (CCDs) covering the whole (4 degree by 4 degree) field of view of the Schmidt telescope, the largest CCD mosaic used in an astronomical camera when built. This instrument was used to produce The Big Picture, the largest astronomical photograph ever produced. [17] The Big Picture is on display at Griffith Observatory.

Current research

Current research programs on the 200-inch Hale Telescope cover the range of the observable universe including studies on near-Earth asteroids, outer solar system planets, Kuiper Belt Objects, star formation, exoplanets, [18] gamma-ray bursts, black holes, quasars and much more. [19]

The 48-inch Samuel Oschin Schmidt Telescope is actively working on a new sky survey, the Zwicky Transient Facility (ZTF). [20]

The 60-inch telescope is used for a variety of projects including follow-up observations for the Palomar Transient Factory and is a rapid response telescope for gamma-ray bursts.

Clearest images

In September 2007, a team of astronomers from the United States and Britain released some of the clearest pictures ever taken of outer space. The pictures were obtained through the use of a new hybrid "Lucky imaging" and "adaptive optics" system that sharpens pictures taken from the Palomar Observatory. The resolution attained exceeds that of the Hubble Space Telescope by a factor of two. [21]


The Palomar Observatory is an active research facility. However, parts of it are open to the public during the day. Visitors can take self-guided tours of the 200-inch telescope daily from 9 a.m. to 3 p.m. The observatory is open 7 days a week, year round, except for December 24 and 25 and during times of inclement weather. Guided tours of the 200-inch Hale Telescope dome and observing area are available Saturdays and Sundays from April through October. There is a visitor's center and a gift shop on the grounds. Behind-the-scenes tours for the public are offered through the community support group, Friends of Palomar Observatory. Periodic tours are also organized by the Reuben H. Fleet Science Center in San Diego. [22] The observatory is located off State Route 76 in northern San Diego County, California, is two hours' drive from downtown San Diego, and three hours' drive from central Los Angeles ( UCLA, LAX airport ). Those staying at nearby Palomar Campground can visit Palomar Observatory by hiking 2.2 miles (3.5 km) up Observatory Trail. [23]

In Episode 5 of Gunbuster, Palomar Observatory is used by the Earth Space Force to collect space imagery intelligence.

In the October 11 and 12, 1989, Calvin and Hobbes comic strips, Calvin has a dream where Stupendous Man takes the lens from the Palomar Observatory telescope (though really the telescope has a mirror and not a lens) and uses it to destroy his school. [24]

Canadian band The Rheostatics' 1992 release Whale Music features a track entitled "Palomar." The song depicts a man named Palomar on the top of a mount, cleaning his lenses with saline waters, and assembling his kaleidoscope in his lonely observatory. The song presents a visual characterization of a man on a mountain and his relationship with his best friend, a dog.

In 1994, Palomar is mentioned in the first episode of season 2 of The X-Files , "Little Green Men". Fox Mulder refers to Hale's suggestion that an elf [25] crawled through his window and told him to build the observatory.

The band Wellwater Conspiracy's 1997 debut album, Declaration of Conformity , contains an instrumental track entitled "Palomar Observatory." Wellwater Conspiracy singer/drummer Matt Cameron grew up in San Diego near the observatory.

Selected books

See also

Related Research Articles

Astrometry part of astronomy, covers star positions and their movements

Astrometry is the branch of astronomy that involves precise measurements of the positions and movements of stars and other celestial bodies. The information obtained by astrometric measurements provides information on the kinematics and physical origin of the Solar System and our galaxy, the Milky Way.

Photographic plate target medium in photography

Photographic plates preceded photographic film as a capture medium in photography. The light-sensitive emulsion of silver salts was coated on a glass plate, typically thinner than common window glass, instead of a clear plastic film.

Charles T. Kowal American astronomer

Charles Thomas Kowal was an American astronomer known for his observations and discoveries in the Solar System. As a staff astronomer at Caltech's Mount Wilson and Palomar Mountain observatories between 1961 and 1984, he found the first of a new class of Solar System objects, the centaurs, discovered two moons of the planet Jupiter, and discovered or co-discovered a number of asteroids, comets and supernovae. He was awarded the James Craig Watson Medal for his contributions to astronomy in 1979.

Jean Mueller is an American astronomer and discoverer of comets, minor planets, and a large number of supernovas at the U.S. Palomar Observatory in California.

4065 Meinel, provisional designation 2820 P-L, is an asteroid from the inner regions of the asteroid belt, approximately 4 kilometers in diameter. It was discovered on 24 September 1960, by Dutch astronomer couple Ingrid and Cornelis van Houten on photographic plates taken by Dutch–American astronomer Tom Gehrels at Palomar Observatory, California. The asteroid was named for American astronomer Aden Meinel.

The National Geographic Society – Palomar Observatory Sky Survey (NGS-POSS) was a major astronomical survey, that took almost 2,000 photographic plates of the night sky. It was conducted at Palomar Observatory, California, United States, and completed by the end of 1958.

Schmidt camera scientific instrument

A Schmidt camera, also referred to as the Schmidt telescope, is a catadioptric astrophotographic telescope designed to provide wide fields of view with limited aberrations. The design was invented by Bernhard Schmidt in 1930.

The Digitized Sky Survey (DSS) is a digitized version of several photographic astronomical surveys of the night sky, produced by the Space Telescope Science Institute between 1983 and 2006.

Samuel Oschin telescope

The Samuel Oschin telescope, also called the Oschin Schmidt, is a 48-inch-aperture (1.22 m) Schmidt camera at the Palomar Observatory in northern San Diego County, California. It consists of a 49.75-inch Schmidt corrector plate and a 72-inch (f/2.5) mirror. The instrument is strictly a camera; there is no provision for an eyepiece to look through it. It originally used 10- and 14-inch glass photographic plates. Since the focal plane is curved, these plates had to be preformed in a special jig before being loaded into the camera.

UK Schmidt Telescope

The UK Schmidt Telescope (UKST) is a 1.24 metre Schmidt telescope operated by the Australian Astronomical Observatory ; it is located adjacent to the 3.9 metre Anglo-Australian Telescope at Siding Spring Observatory, Australia. It is very similar to the Samuel Oschin telescope in California. The telescope can detect objects down to magnitude 21 after an hour of exposure on photographic plates.

The Quasar Equatorial Survey Team (QUEST) is a joint venture between Yale University, Indiana University, and Centro de Investigaciones de Astronomia (CIDA) to photographically survey the sky using a digital camera, an array of 112 charge-coupled devices. Since 2009, it has used the 1 m ESO Schmidt Telescope in Chile. From 2003–2007, it used the 48 inch (1.22 m) Samuel Oschin telescope at the Palomar Observatory. Before that, it had used the 1.0-metre Schmidt telescope at the Llano del Hato National Astronomical Observatory in Venezuela.

Llano del Hato National Astronomical Observatory

The Llano del Hato National Astronomical Observatory is an astronomical observatory in Venezuela. It is 3600 meters above sea level and is the country's main observatory. It is situated above the village of Llano del Hato in the Venezuelan Andes, not far from Apartaderos which lies about 50 kilometers north-east of Mérida, Mérida State.

6805 Abstracta, provisional designation 4600 P-L, is a carbonaceous Themistian asteroid and slow rotator from the outer region of the asteroid belt, approximately 10 kilometers in diameter.

10660 Felixhormuth, provisional designation 4348 T-1, is a background asteroid from the outer regions of the asteroid belt, approximately 7 kilometers in diameter. It was discovered on 26 March 1971, by Dutch astronomer couple Ingrid and Cornelis van Houten at Leiden, on photographic plates taken by Dutch–American astronomer Tom Gehrels at Palomar Observatory in California, United States. The asteroid was named after German astronomer Felix Hormuth.

1924 Horus, provisional designation 4023 P-L, is a dark asteroid from the inner regions of the asteroid belt, approximately 12 kilometers in diameter. Discovered during the Palomar–Leiden survey in 1960, it was later named after Horus from Egyptian mythology.

The Palomar Transient Factory, was an astronomical survey using a wide-field survey camera designed to search for optical transient and variable sources such as variable stars, supernovae, asteroids and comets. The project completed commissioning in summer 2009, and continued until December 2012. It has since been succeeded by the Intermediate Palomar Transient Factory (iPTF), which itself transitioned to the Zwicky Transient Facility in 2017/18. All three surveys are registered at the MPC under the same observatory code for their astrometric observations.

The Palomar–Leiden survey (PLS) was a successful astronomical survey to study faint minor planets in a collaboration between the U.S Palomar Observatory and the Dutch Leiden Observatory, and resulted in the discovery of thousands of asteroids, including many Jupiter trojans.

Christine D. Wilson is a Canadian-American physicist and astronomer, currently a University Distinguished Professor at McMaster University.

The Zwicky Transient Facility is a wide-field sky astronomical survey using a new camera attached to the Samuel Oschin Telescope at the Palomar Observatory in California, United States. Commissioned in 2018, it supersedes the (Intermediate) Palomar Transient Factory (2009–2017) that used the same observatory code. It is named after the astronomer Fritz Zwicky.


  1. Cornell University, Dept. of Astronomy: Palomar Observatory
  2. Super Camera of the Skies." Popular Mechanics, April 1942, p. 52.
  3. "60th Anniversary of Hale Telescope," 365 Days of Astronomy (podcast). January 26, 2009.
  4. International Dark-Sky Association Archived 2008-01-01 at the Wayback Machine (IDA): "Sky Glow Effect on Existing Large Telescopes", IDA Info #20.
  5. "Caltech Astronomy – The 200-inch Hale Telescope". Caltech Astronomy. Retrieved 2014-12-09.
  6. "Caltech Astronomy – The 60-inch Telescope". Caltech Astronomy. Retrieved 2014-12-09.
  7. "Caltech Astronomy – Samuel Oschin Telescope". Caltech Astronomy. Retrieved 2014-12-09.
  8. "Caltech Astronomy – Discoveries from Palomar Observatory's 48-inch Samuel Oschin Telescope". Caltech Astronomy. Retrieved 2014-12-09.
  9. "Caltech Astronomy – The 18-inch Schmidt Telescope". Caltech Astronomy. Retrieved 2014-12-09.
  10. "Caltech Astronomy – Palomar Testbed Interferometer (PTI)". Caltech Astronomy. Retrieved 2014-12-09.
  11. "Caltech Astronomy – Sleuth: The Palomar Planet Finder". Palomar Skies. Retrieved 2014-12-09.
  12. Caltech did recognize Fritz Zwicky's sky survey pioneering work; however, The Big Picture project failed to recognize his contribution to the sky survey technique in the introductory panel at the Griffith Observatory.
  13. Minnesota Automated Plate Scanner (MAPS): MAPS catalogue; Mollise, Rod. (2006). The Urban Astronomer's Guide: a Walking tour of the Cosmos for City Sky Watchers, p. 238. , p. 238, at Google Books
  14. Caltech: The Second Palomar Observatory Sky Survey (POSS II) Archived 2009-05-16 at the Wayback Machine
  15. NASA/Space Telescope Science Institute (STScI).: Multimission Archive at STScI (MAST)
  16. Caltech press release: "New Sky Survey Begins at Palomar Observatory." July 29, 2003.
  17. Caltech: "The Big Picture" Archived 2007-02-04 at the Wayback Machine
  18. JPL: "Planet-Hunting Method Succeeds at Last." May 28, 2009.
  19. Caltech: Hale Telescope Observing Runs Archived 2012-12-12 at
  20. Caltech: Zwicky Transient Facility (ZTF)
  21. Ghosh, Pallab. "'Clearest' images taken of space," BBC. September 3, 2007; University of Cambridge, Institute of Astronomy, Lucky Imaging website
  22. Reuben H. Fleet Science Center: Palomar Observatory tour Archived 2003-04-11 at the Wayback Machine
  23. "Observatory Trail in Cleveland National Forest". Hikespeak. Retrieved March 28, 2017.
  24. Biography of George Ellery Hale at

Further reading