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Astronomy and Astrophysics
Yerkes Observatory
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Yerkes Observatory
Yerkes Observatory Williams Bay, Wisconsin.
Front View, 1988.
(Photo Credit: Yerkes Observatory)

Name:Yerkes Observatory
Location:Williams Bay, Wisconsin
Classification:Private, building

Areas of Significance:National Register: education, engineering, NHL: science, Subtheme: physical science, Facet: astronomy

Builder:Henry Ives Cobb


Yerkes Observatory is the observing facility of the Department of Astronomy and Astrophysics of the University of Chicago and is devoted to research in astronomy and astrophysics, as well as graduate education. The observatory is on the west side of the village of Williams Bay, Wisconsin, on the bank of Lake Geneva, 76 miles from Chicago. Construction of the main observatory building began in 1895. The first astronomical observations were made in the summer of 1897. At the time of its construction, Yerkes Observatory was the most modern and complete observatory of its day. [1]

The observatory was designed by Henry Ives Cobb from plans drawn by American astronomer George Ellery Hale, who had visited the large observatories of America and Europe and had gained useful information from the designs of the Lick Observatory in California and the Astrophysical Observatory at Potsdam, Germany. The style of the building is Romanesque with elaborate details. It is constructed of brown Roman brick with terra cotta ornaments to match. The shape is that of a Latin cross with the three towers and the meridian room at the extremities. The long axis lies east and west with the great dome to the west. The length of the building in this direction is 326 feet. The smaller domes are on the north-and-south axis, with their centers 144 feet apart.

The principal floor contains offices for the staff, a lecture room, a large reference library, and a reading room. The basement contains darkrooms, a photographic laboratory, a machine shop, and maintenance rooms. The second floor is used for stackrooms for library books, storage of archival materials, sleeping rooms for observers, and a large analysis room where an electronic computer is found. A glass copy of the National Geographic-Palomar Observatory Sky Survey is also stored and used on this floor. An environmentally controlled vault, for the storage and preservation of the observatory's irreplaceable collection of photographs taken over the years with the telescopes at Yerkes, occupies the east end of the main and second floors.

Situated at the eastern end of the building are two small domes and a small meridian transit room. The northern dome originally contained George Ellery Hale's 12-inch refractor from his old Kenwood Observatory in Chicago. The southern dome contains a 24-inch reflector telescope. These telescopes have been replaced with newer, more modern telescopes. The northern dome now houses a modern 24-inch reflector; the southern dome houses a 41-inch reflector placed in operation in 1968. The meridian room, although intact, is no longer operational.

The great dome, housing the 40-inch refractor, is on the western end of the building. This telescope is the largest refractor ever completed, with a gain of 4 inches aperture and 23% in light-gathering ability over its nearest rival, the 36-inch refractor at Lick Observatory in California. The 40-inch glass lens for the refractor was cast by the firm of Mantois in Paris and ground by Alvan G. Clark. The telescope tube, mounting, dome, and rising floor were designed by the firm of Warner & Swasey of Cleveland, Ohio.

The telescope is mounted on a massive brick pier which rests on a solid concrete foundation set in a gravel formation. The column is of cast iron in four heavy sections. The center of motion of the telescope is 61 feet above the ground; when the spectroscopic attachments are added, this is increased by nearly 6 feet.

The telescope is moved from one position to another by means of electric motors and is so finely balanced that it can be moved by hand. The entire telescope weighs 20 tons. For finer motions, such as required in spectroscopic and photographic work, additional motors, controlled from the position of the observer, are used. The telescope was modernized in 1969 permitting more accurate and rapid setting of the position of the telescope. The efficiency of the telescope was further increased by the addition of an automatically guiding camera. The driving clock, by which the telescope is made to follow the stars, consists of a synchronous motor controlled by an electronic oscillator, the frequency of which can he set so as to make the telescope follow the sun, the moon, or stars.

The dome covering the 40-inch refractor is 90 feet in diameter. It is turned on 26 wheels by an electric motor which actuates an endless wire rope extending around the dome. The original dome surface, made of wood covered by a thin sheet of metal, was replaced by stainless steel in 1975. The opening through which the sky is observed is 11 feet wide, and is closed by shutters 85 feet long. These are so constructed that they can be moved by hand, although they are usually operated by an electric motor. Canvas screens, which may be raised over part of the opening, serve to break the force of the wind. The rising floor is 75 feet in diameter and is supported by cables running over four sheaves just beneath the upper balcony and connecting heavy counterpoises which balance the weight of the floor (37-1/2 tons). The motors for moving the dome and the floor can be operated from the floor or the eye end of the telescope. The floor moves through a range of 23 feet from the lower to the upper balcony. It has to be near its lowest point when a star near the zenith is observed. In intermediate positions it can be quickly adjusted to any height from the eyepiece of the telescope.


Yerkes Observatory was founded by American astronomer George Ellery Hale in 1897 and represents his revolutionary concept for an observatory that would also be a physical laboratory. To the majority of astronomers at the time, an observatory was simply a place for a telescope and observer. For example, when the new United States Naval Observatory in Washington, DC was completed in 1893 there was no provision for a darkroom or for a spectroscopic laboratory. In contrast, Yerkes Observatory was provided with laboratories and a variety of mechanical and electronic workshops. Yerkes represented the wave of the future and established the modern observatory as a research institution where the astronomer, using the disciplines of chemistry and physics, supported by engineering and optics workshops, could apply his talents to the understanding of the wonders of the universe. In the years since its founding by George Ellery Hale, Yerkes has attracted the most famous astronomers in the world, and contributed significantly to the sciences of astronomy and astrophysics. [2]


The establishment of Yerkes Observatory near the city of Chicago was the joint idea of astronomer George Ellery Hale and William Harper, president of the University of Chicago. George Ellery Hale, then a recent physics graduate from M.I.T., wanted a first-rate observatory where he could continue his study of the sun. Hale wanted to bring into being his concept of a modern observatory that would serve not only as an observing facility for astronomers but also as a first rate research facility where scientists could study the skies using the interdisciplinary skills of the astronomer, physicist and chemist, supported by workshops employing people with skills in optics, photography, mechanics, carpentry, and electronics. Of all of these skills, Hale believed, a knowledge of physics was the most important for the study of astronomy. Hale's application of physics to the study of astronomy was soon to give birth to a new field of study--astrophysics.

William Harper, as the president of the newly founded University of Chicago, was more concerned with increasing the reputation of the university through the establishment of a first-rate research laboratory, which would attract the best minds in the field of astronomy and bring recognition and honor to his school. Yerkes was to be successful in both regards. [3]

In the summer of 1892 George Ellery Hale learned that a pair of 40-inch diameter glass disks, made by the Paris firm of Mantois, were available for purchase. Alvan G. Clark, the great telescope maker of Cambridge, Massachusetts had tested the glass disks and found them perfect. Hale realized that this was an opportunity to build the largest telescope in the world and approached Harper with the idea. Harper agreed to support the project if a donor could be found to support the grinding of the lens and the building of an observatory. In September 1892 both men visited Charles T. Yerkes, a Chicago street-car magnate, who agreed to underwrite the cost of the project. Eventually, George Ellery Hale had to talk Yerkes into parting with $349,000 before the project was completed. [4]

Progress on the new observatory moved quickly after Yerkes made his commitment. The glass disks were purchased for $20,000 and Alvan Clark began the long process of grinding them into the proper shape. The mechanical parts of the telescope were completed in 1893 in time for exhibition at the Columbian Exposition in Chicago. By October 1895 the glass lenses were completed and tested by Hale, who found them excellent.

Construction of the observatory building was begun in 1895 at Williams Bay, Wisconsin, distant enough from the smoke, haze and dust of Chicago (76 miles) to assure dark skies, and yet close enough to the city to be readily accessible to the faculty and students of the University of Chicago. The first astronomical observations with the completed telescope were made by Hale and his associates in the summer of 1897. The excellent optical qualities of the new telescope were immediately proven when astronomer Edward Emerson Barnard soon discovered a faint third companion to the star Vega, which had gone undetected even by the skilled astronomer Sherburne W. Burnham using the 36-inch Lick telescope.

Hale was successful in his quest. The new Yerkes Observatory not only possessed the largest telescope but was the most modern and complete observatory in the country. Hale had seen to it that the instrumentation at Yerkes was second to none.

Soon Yerkes began to attract the foremost astronomers in both America and Europe. Sherburne W. Burnham continued his work, begun at Lick, in cataloging double stars. With the new 40-inch refractor he was able to measure thousands of neglected and overlooked star pairs, adding precious data to the meager store of information on stellar masses. In 1906 with Hale's support, Burnham published his General Catalog of Double Stars within 121 of the North Pole. This great catalog contained data on 13,665 double and multiple star systems and gave a major boost to double and multiple star astronomy.

Utilizing a fast photographic lens, Edward Barnard took photographs that were compiled into the Photographic Atlas of Selected Regions of the Milky Way, a work that remains a landmark in the study of our galaxy. From 1905-1927 Barnard discovered and mapped the large dark clouds of the Milky Way.

George Ellery Hale continued his own research on the sun at Yerkes with the completion of his spectroheliograph in the Yerkes instrument shop. With this instrument he proved that calcium and hydrogen flocculi seen on the solar disk were vast prominences thrown off by the activity in the Sun's outermost layers.

Ernest Nichols arrived at Yerkes in the summer of 1898 with a radiometer to determine the heat from the stars. Mounted in the heliostat room, the device successfully measured the near-infrared radiation of Arcturus and Vega.

Spectroscopist Walter Adams joined the staff at Yerkes in 1898 and worked with Edwin Frost to measure the radial velocities of B-type stars. Albert Michelson, in experiments at Yerkes, measured double stars with his interferometer while Frank Schlesinger pioneered the photographic determination of stellar parallax, increasing by a factor of 10 the accuracy of distance measurements over those made by visual observations.

Among the other prominent staff members were the optician Frank Ross who introduced the wide-angle lens as an important photographic tool in astronomy. George Ritchey, another Yerkes optical designer, demonstrated how the visually color-corrected 40-inch refractor could be used photographically as well by placing a yellow filter in front of a special photographic plate.

Despite the success of Yerkes, Hale was not satisfied and eventually began to look to California as a site for newer and larger telescopes. During the winter of 1903-04 Hale traveled to Pasadena, California to investigate the possibility of establishing an observatory on Mount Wilson. Once he was satisfied with the new site Hale returned to Yerkes to persuade many of his friends on the staff to join him. Even after Hale's departure, Yerkes continued to attract some of the finest astronomers in the world and produce new information in the study of astronomy.

Astronomer George van Biesbroeck began a program of positional observations of comets and asteroids with the 24-inch reflector. John Parkhurst worked to perfect photometric scales of stellar magnitudes. In 1913 Edwin Hubble worked at Yerkes photographing faint galaxies--a field of research that was to lead him eventually to Mount Wilson, where he was to formulate his concept of the size and nature of the universe. Frank Ross's work in photography began to reveal the faint features of interstellar matter in the galaxy. In the 1930s Otto Struve arrived at Yerkes as a graduate student and stayed eventually to become director. Struve was a superb spectroscopist and made detailed studies of stellar atmospheres, stellar rotation, and binary stars. In 1930 another graduate student, William Wilson Morgan, stayed at Yerkes and worked to determine the distances and luminosities of stars from their spectra. Morgan's work would eventually lead to the discovery of the spiral structure of our galaxy. Astronomer Gerard Peter Kuiper arrived at Yerkes in 1936 as a member of the faculty of the University of Chicago. In 1944, through his research, Kuiper discovered the atmosphere on Titan, a satellite of Saturn. In 1948 Kuiper discovered the fifth satellite of Uranus and in 1949 the second satellite of Neptune.

The Yerkes Observatory, in the century since its establishment by George Ellery Hale, has had a profound impact on the history of the sciences of astronomy and astrophysics. The Yerkes Observatory not only established the format of the modern research observatory but was also the scene for many of the major scientific discoveries in the past century in these fields. In addition, the legions of astronomers who were trained at Yerkes have gone on to work in and, in many cases, direct other observatories, planetaria, and departments of astronomy and astrophysics. Several names readily come to mind: Edwin P. Hubble, who worked on the recession of galaxies, thereby first giving evidence of the expansion of the universe; Walter S. Adams, later the director of Mount Wilson Observatory who did pioneering work in the study of stellar spectra; and William H. Wright, who became the director of Lick Observatory.

George Ellery Hale's plan for Yerkes Observatory was so precise in detail and so broad in scope that he forever changed the science of astronomy and the concept of the modern observatory. Years after its establishment, Yerkes astronomers would say: "Only now are we carrying out many of the ideas Hale planned for. His vision was extraordinary." [5]


1. The descriptive material in this section was taken from the following sources:

University of Chicago, "Yerkes Observatory" (U.S.A.: no publisher identified, no date).

Bruce Bond, "A Celebration of Light: Yerkes in Perspective," Astronomy Magazine, December 1982, pp. 6-22.

2. Helen Wright, Explorer of the Universe: A Biography of George Ellery Hale (New York: E.P. Dutton & Co., Inc., 1966), pp. 108-11.

3. The historical background for this section was taken from the following sources:

"Yerkes Observatory" op. cit.

Bruce Bond, op. cit., pp. 6-22.

4. Richard Learner, Astronomy Through the Telescope (New York: Van Nostrand Reinhold Company, 1981), p. 104.

5. Wright, op. cit., 111.


Abell, George O. Exploration of the Universe. 4th ed., Philadelphia: Saunders College Publishing, 1982.

Asimov, Isaac. Eyes On The Universe. Boston: Houghton Mifflin Company, 1975.

Bond, Bruce. "A Celebration of Light: Yerkes in Perspective," Astronomy Magazine, December 1982, pp. 6-22.

Kirby-Smith, H.T. U.S. Observatories: A Directory and Travel Guide. New York: Van Nostrand Reinhold Company, 1976.

Learner, Richard. Astronomy Through the Telescope. New York: Van Nostrand Reinhold Company, 1981.

Morgan, W. W. "Yerkes Observatory (1897-1941)," Telescopes: How to Make and Use Them. Vol.4., New York: Macmillan Company, no date, pp. 273-76.

Staff, Yerkes Observatory. "Facts Sheet: Observational Discoveries of Historical Importance." No date.

University of Chicago. Yerkes Observatory., no date.

Wright, Helen. Explorer of the Universe: A Biography of George Ellery Hale. New York: E. P. Dutton & Co., Inc., 1966.


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