Hale Constructs the 200-Inch Telescope Summary

  • Last updated on November 10, 2022

George Ellery Hale constructed what was then the world’s largest telescope, enabling scientists to study more of the universe and to refine their measurements and observations of those celestial objects that were already known.

Summary of Event

George Ellery Hale was born in Chicago on June 29, 1868. He pursued his education at the Massachusetts Institute of Technology and graduated in 1890. During that same year, Hale founded the Kenwood Astrophysical Observatory Kenwood Astrophysical Observatory near his Chicago home. Hale conducted research in solar spectroscopy (the analysis of the sun’s light) and developed, in 1891, a device called the spectroheliograph Spectroheliograph , an instrument that photographs the sun in a narrow wavelength band. (These types of photographs reveal the structure of the sun’s surface.) In 1892, Hale became the first director of the Yerkes Observatory, Williams Bay, Wisconsin, and received funding for a 102-centimeter refracting telescope. He always envisioned working in an astronomy department with state-of-the-art observational equipment. Hale was one of the founders, in 1895, of a professional publication known as the Astrophysical Journal. Several years later, in 1899, he helped establish the American Astronomical Society. [kw]Hale Constructs the 200-Inch Telescope (June 3, 1948) [kw]200-Inch Telescope, Hale Constructs the (June 3, 1948)[Two hundred Inch Telescope, Hale Constructs the] [kw]Telescope, Hale Constructs the 200-Inch (June 3, 1948) Hale telescope Telescopes;optical Astronomy;telescopes Hale telescope Telescopes;optical Astronomy;telescopes [g]North America;June 3, 1948: Hale Constructs the 200-Inch Telescope[02530] [g]United States;June 3, 1948: Hale Constructs the 200-Inch Telescope[02530] [c]Astronomy;June 3, 1948: Hale Constructs the 200-Inch Telescope[02530] [c]Science and technology;June 3, 1948: Hale Constructs the 200-Inch Telescope[02530] [c]Engineering;June 3, 1948: Hale Constructs the 200-Inch Telescope[02530] Hale, George Ellery Thomson, Elihu Adams, Walter Sydney Fosdick, Raymond Carnegie, Andrew

Not only was Hale an inventor and astronomer, but he also had the fortunate ability to be an excellent fund-raiser. He continued to dream of bigger and better astronomical equipment. Hale made presentations before members of the Carnegie Institute of Washington to advise them of the unusual opportunity of building an observatory in the nearly cloudless mountains of Southern California. In 1904, he received a grant from Andrew Carnegie of the Carnegie Institute for construction of the Mount Wilson Observatory Mount Wilson Observatory (near Los Angeles, California), where 152-centimeter (in 1908) and 254-centimeter (in 1917) reflecting telescopes were erected. Hale served as director of Mount Wilson Observatory until 1923.

Yet, Hale continued to dream of a larger telescope. By 1928, he had written many articles describing the benefits of constructing a giant telescope. He sent copies of his articles to representatives of the Carnegie Institute Carnegie Institute and Rockefeller Foundation Rockefeller Foundation , hoping to arouse financial support. Hale negotiated a highly unusual financial cooperation between these foundations for the construction and future operation of a 508-centimeter (200-inch) telescope. The staff from Mount Wilson Observatory (funded by the Carnegie Institute) would supply scientists to construct and operate the telescope, while the California Institute of Technology California Institute of Technology (funded by the Rockefeller Foundation) would organize the utilization of the telescope.

Raymond Fosdick, then president of the Rockefeller Foundation, appropriated $6 million for the construction of the new 508-centimeter telescope. The California Institute of Technology (Caltech) provided an endowment for operation of the telescope. On October 29, 1928, Hale announced construction plans for the telescope to the media.

Hale was sixty years old when he received the funds to start building his dream of a telescope. His health, however, was not good; his stressful lifestyle caused Hale to be hospitalized for a short time in a sanatorium. Afterward, he strove to take life at a slower pace but continued to assist with the plans for the telescope. He had to solve several problems: where to build the new observatory and how to cast a 508-centimeter mirror.

Hale had originally planned to place the new telescope at Mount Wilson Observatory. He found that light pollution (light glow from Los Angeles) had increased to the point that the skies were not as dark as when the observatory was initially built. He then considered putting the telescope in the Southern Hemisphere but believed that it would be too remote from other major observatories. Instead, he investigated sites in the Northern Hemisphere.

Hale brought small telescopes to many prospective sites and noted the quality of the star images: whether they were steady and sharp. Specialized instruments measured the amount of sunny days and wind speed and direction for approximately five years. Hale and his colleagues finally decided on Mount Palomar, an area between San Diego and Pasadena, California. Geologists from the California Institute of Technology surveyed the terrain around Mount Palomar and determined the exact location on which the telescope should be built. On September 21, 1934, the land on Mount Palomar was purchased from local ranchers. An official groundbreaking ceremony was held on August 18, 1935.

Another problem to be tackled was the feasibility of casting a 508-centimeter (diameter) mirror. This particular-sized mirror would be larger and wider than any mirror previously made. The ideal glass was thought to be quartz, as it would expand or contract very little through variations in temperature. Elihu Thomson, a scientist at the General Electric Company in Lynn, Massachusetts, was contracted to cast the 508-centimeter quartz disk. Unfortunately, each time the quartz was heated, evaporation caused bubbles to form. The possibility of using quartz was finally abandoned in 1931.

Members of the Observatory Council, including Walter Sydney Adams (director of Mount Wilson Observatory), asked the Corning Glass Works, in Corning, New York, to develop a 508-centimeter Pyrex disk. (Pyrex is a low-expansion borosilicate glass.) Although temperature variations affect Pyrex more than quartz, it is still easier to work with than ordinary glass. A special annealing oven was built, and the 508-centimeter mirror was poured successfully on December 2, 1934. The Pyrex disk was cast as a hexagonal cellular structure. Thus, the disk was only about half the weight it would have been as a solid. It remained in New York for almost two years before it was crated for its westbound trip.

The 508-centimeter disk was packed and loaded aboard a New York Central Railway car. The cross-country trek (between Corning, New York, and Pasadena, California) began on March 26, 1936. The train moved at a speed of only 40 kilometers per hour and only during daylight hours, to avoid excessive vibrations and stress on the glass. Upon the mirror’s arrival in Pasadena on April 10, it was brought to the optical shop at Caltech for polishing.

A unique “horseshoe” mounting for the mirror was designed by physicists at Caltech, so that the mount would remain stationary when the telescope was turned. The weight of the mount was estimated to be 600,000 pounds. A benefit of this particular mounting was that the telescope could be pointed toward high northern latitudes of the sky, a term known as “declination.” The 254-centimeter telescope at Mount Wilson was built with such a restrictive mount.

The 508-centimeter telescope was also constructed to be a “prime focus” instrument. That is, the observer actually climbs into a cage within the telescope and observes light reflected from the mirror onto a photographic plate. A platform moves up and down so the astronomer can step directly into the prime focus area. This telescope is one of the few that allows the observer to view from the prime focus, rather than from an eyepiece below the body of the instrument.

On February 21, 1938, Hale died before his dream of the 508-centimeter telescope could be completed. The occurrence of World War II caused optical astronomy to come almost to a halt. Many scientists who had worked on Mount Palomar were contracted into the war effort. Finally, on June 3, 1948 (ten years after Hale’s death), the 508-centimeter telescope was officially dedicated and named the Hale telescope, a monument to the man whose vision and leadership made it a reality.


Hale’s dream of building the largest telescope in the world was conveyed to both the private and public sectors. He was a genius at acquiring financial support from private foundations, and his colleagues were intrigued by his plans. Many astronomers envied Hale, while others were unsure of the possibility of constructing such a large telescope.

The general public and press followed the progress of this new telescope with great anticipation. Headlines in major newspapers provided up-to-the-minute news on the status of the mirror and dome construction. When the telescope was finally dedicated, the astronomical community prepared with excitement for the new views of the heavens that lay ahead.

In designing the 508-centimeter telescope, Hale sought to supplement the equipment of nearby Mount Wilson Observatory and provide information to other observatories to assist in the development of new experimental technology. He also foresaw that this telescope would be capable of making detailed observations of high northerly situated stars and galaxies. (The Mount Wilson 254-centimeter telescope was restricted from observing near the north celestial pole.)

The cross-country trek of the 508-centimeter mirror was publicly visible. The media spread the latest news of the mirror’s journey. Thousand of people gathered along the train route to see the precious cargo. Children were even dismissed early from school to catch a glimpse of this historic event.

One of the first observations made with the Hale telescope led to a doubling of the distance scale between the Milky Way and Andromeda galaxies, from 1 to 2 million light-years. The importance of a detailed investigation of neighboring galaxies is in establishing a schematic of the distribution of galaxies. In addition, a spectroscopic study of galaxies (that is, an analysis of the light given off by them) allows for measurements of their speeds and whether those galaxies are receding from or moving toward the Milky Way. In fact, observations made with the Hale telescope have suggested that the universe is still expanding (from the original big bang of about 15 billion years ago).

Observations taken on the 508-centimeter telescope are not solely the property of a selective group of scientists but are available to persons interested in studying them. It may be the astronomers who take the actual photographs or measurements, but this information is relayed through the media and toward the general public. Though the Hale telescope stimulates more questions than it answers, it is a very powerful instrument—developed by a person who had a dream and never ceased to pursue it. The name “Hale telescope” is a reminder to both the general public and scientific community of their debt to Hale.

The telescope remained the largest in the world from 1948 until 1976, when the 600-centimeter reflector was completed at Zelenchukskaya, in the Soviet Union, following which numerous, even larger telescopes were built, including the Keck, Gemini North, and Subaru Telescopes at Mauna Kea, Hawaii; The Very Large Telescope and Gemini South Telescope in Chile, the Multiple Mirror Telescope at Mt. Hopkins Arizona, and the Large Binocular Telescope at Mt. Graham, Arizona, as well as even larger telescopes at the Canary Islands and in South Africa. Hale telescope Telescopes;optical Astronomy;telescopes

Further Reading
  • citation-type="booksimple"

    xlink:type="simple">Asimov, Isaac. Eyes on the Universe. Boston: Houghton Mifflin, 1975. A general history of the telescope is outlined in this useful reference. From the beginnings of its use by Galileo through the construction of Mount Palomar Observatory and the future of orbiting satellites, the telescope is seen changing through the times.
  • citation-type="booksimple"

    xlink:type="simple">Bolton, Nancy. “Press Pilgrimage to Palomar.” Sky and Telescope 7 (January, 1948): 59-63. The incredible journey of the 508-centimeter mirror from Pasadena to Mount Palomar is seen through the eyes of a magazine reporter. Photographs depict the actual packing and transportation of the precious mirror along the rocky dirt roads of Southern California in this nostalgic article.
  • citation-type="booksimple"

    xlink:type="simple">Coles, Robert. “The 200-Inch Telescope.” Sky and Telescope 7 (September, 1948): 267-269. This article was written at the time of the dedication of the Hale telescope. A photograph of the 508-centimeter dome as well as photographs of the telescope mount are highlighted. The author details the excitement between the public and the astronomical community and discusses future uses of the Hale telescope.
  • citation-type="booksimple"

    xlink:type="simple">Di Cicco, Dennis. “The Journey of the 200-Inch Mirror.” Sky and Telescope 17 (April, 1986): 347-348. This article details the voyage of the 508-centimeter mirror aboard the New York Central Railway. A detailed diagram lists all the major stops along the route, from Corning, New York, to its final destination in Pasadena, California. Two archival photographs supplement the article.
  • citation-type="booksimple"

    xlink:type="simple">Shapley, Harlow, ed. Source Book in Astronomy, 1900-1950. Cambridge, Mass.: Harvard University Press, 1960. This text is an excellent reference for many great historical moments in astronomy. Chapter 1, “The 200-Inch Reflector on Mount Palomar,” is particularly relevant to the fund-raising for and final construction of the Hale telescope; the remainder of the text is an outstanding general reference.
  • citation-type="booksimple"

    xlink:type="simple">Woodbury, David. The Glass Giant of Palomar. New York: Dodd, Mead, 1953. This is the text for the reader who wants to know the details of the 508-centimeter mirror of the Hale telescope. The text is supplemented with several hand-drawn sketches as well as black-and-white photographs.
  • citation-type="booksimple"

    xlink:type="simple">Wright, Helen. Explorer of the Universe: A Biography of George Ellery Hale. New York: E. P. Dutton, 1966. The entire text is a chronology of Hale’s life, beginning with his childhood in Chicago, his directorship of the Yerkes and Mount Wilson observatories, and his true quest to build the world’s largest reflecting telescope. The personal side of Hale is reflected through photographs of his family and colleagues.
  • citation-type="booksimple"

    xlink:type="simple">_______. Palomar: The World’s Largest Telescope. New York: Macmillan, 1952. This small book covers the actual planning stages through the final completion of construction. Hale’s negotiations with private funding sources are covered along with his great enthusiasm to make the 508-centimeter telescope the best in the world. An extremely detailed photograph of the Hale telescope is presented in the text.
  • citation-type="booksimple"

    xlink:type="simple">Zirker, J. B. An Acre of Glass: A History and Forecast of the Telescope. Baltimore: Johns Hopkins University Press, 2005. The Hale telescope takes pride of place in this history: it represents the transition point between the first three hundred years of telescope development and the modern age of telescopic science.

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