Hale Establishes Mount Wilson Observatory

George Ellery Hale built several telescopes that served as tools for observation and developed new techniques for building more powerful telescopes.

Summary of Event

In the late nineteenth century, observational astronomy had not advanced far beyond Galileo’s first telescope in either power or design. The majority of the powerful telescopes were still small, refracting designs. These telescopes were very similar to those used by ship captains; each contained a fixed eyepiece lens and an adjustable lens that could be positioned to focus the light of an image onto the eyepiece. Larger, more powerful reflecting telescopes were being designed and built; in such a telescope a concave mirror is used to collect light from an object and focus the light onto a series of lenses or an adjustable eyepiece. The telescopes of this period were still individual instruments, primarily powerful eyes without any ability to analyze the visual information they received. Other instruments of physics and chemistry had not yet been coupled with telescopes to exploit their powerful view of the universe. Mount Wilson Observatory
Solar astronomy
[kw]Hale Establishes Mount Wilson Observatory (1903-1904)
[kw]Mount Wilson Observatory, Hale Establishes (1903-1904)
[kw]Wilson Observatory, Hale Establishes Mount (1903-1904)
[kw]Observatory, Hale Establishes Mount Wilson (1903-1904)
Mount Wilson Observatory
Solar astronomy
[g]United States;1903-1904: Hale Establishes Mount Wilson Observatory[00640]
[c]Science and technology;1903-1904: Hale Establishes Mount Wilson Observatory[00640]
[c]Astronomy;1903-1904: Hale Establishes Mount Wilson Observatory[00640]
Hale, George Ellery

After graduating from the Massachusetts Institute of Technology in 1890, George Ellery Hale moved to Chicago. At MIT, Hale had access to the 15-inch (38-centimeter) refracting scope at Harvard and the experience of Harvard’s astronomers. In Chicago, Hale became involved in the building of a 40-inch (102-centimeter) reflecting telescope. The telescope was built at Lake Geneva, Wisconsin, in conjunction with William Rainey Harper, president of the University of Chicago; major funding was provided by Charles Yerkes. In 1903, with the success of the Yerkes telescope, Yerkes telescope Hale left Chicago to establish an observatory at Mount Wilson, California.

George Ellery Hale in his Mount Wilson office.

The building of an observatory at Mount Wilson was initially funded by the Carnegie Institution of Washington. The decision to build the observatory atop Mount Wilson was based on the mountain’s elevation, terrain, and proximity to Pasadena. The elevation was considered ideal because it placed the observatory above the clouds, which otherwise would interfere with viewing. This location, more than a mile above the bordering valley, afforded the observatory additional clear days for observing.

Another key feature of the mountain was the large amount of trees and other plant life growing there. This vegetation helped to absorb radiant heat; that is, most of the heat reflected from the earth was absorbed by the mountain’s abundant foliage. This ability of the mountain to absorb heat meant that the observatory could be designed for both stellar and solar observation. Solar observation is easily hindered by waves of heat reflecting back from the earth and distorting the rays of light coming into a solar telescope. The Mount Wilson site minimized this problem.

The third advantage of the Mount Wilson site was its proximity to Pasadena, home of the recently established California Institute of Technology. California Institute of Technology Pasadena was also a major city with access to rail transportation, many large manufacturing companies, and industrial shops. It was an ideal location for the workshops and business offices of the Mount Wilson Observatory.

The first project Hale undertook was the moving of the Snow solar telescope Snow solar telescope to Mount Wilson. The telescope was disassembled at the Yerkes Observatory Yerkes Observatory in Williams Bay, Wisconsin, where it had been built, and the parts were shipped to Pasadena and transported up the mountain to be reassembled. The pieces arrived in Pasadena by train, but the trip up the mountain was a more primitive journey, involving mules and wagons struggling up winding dirt roads, often delayed by accidents along the route.

When the Snow telescope was rebuilt and began observations near the end of 1903, Hale immediately encountered his first major design problem. The telescope was horizontally designed and rested on the ground in the midst of heat waves reflected off the earth. The California heat became so intense during the middle part of the day that the mirrors of the telescope expanded and distorted, and observation had to be limited to early morning and evening. Hale was disappointed by this brief amount of observation time and also by the quality of the images the telescope was producing. He hypothesized that elevating the telescope would bring it out of the most intense waves of heat and provide cleaner images. To test his idea, he climbed a tall evergreen with a small telescope in hand and compared the image he saw from the top of the tree with the one he had observed at its foot. The experiment convinced him that he was correct in his theory, and he began construction of a trial elevated solar telescope.

This new telescope was built as a 60-foot (18-meter) tower. That is, the tower itself was the telescope, and its immovable nature required Hale to rethink traditional telescope designs. The final version of the telescope consisted of a rotating dome atop the tower that housed a mirror for gathering light. This light was reflected down a shaft to the base of the tower, where it was focused by a series of lenses and mirrors. Hale’s innovative design was a great success, allowing solar observers to track the Sun across its path for the duration of the day. In addition, the reduction in the waves of heat that reached the gathering mirror 60 feet above the earth provided observers with more detailed images than they had previously seen. The success of this tower led to the construction of a more powerful 150-foot (46-meter) tower.

After building the solar towers, Hale added spectrographs to analyze the data collected by the telescopes. A spectrograph Spectrography breaks light down into its component parts, which scientists can then analyze to determine the nature of the chemical reactions and components of the light-producing bodies. The spectrographs at Mount Wilson allowed the scientists to observe the Sun and to see what it is made of. In order to maintain a constant temperature for the spectrographs, which is critical to their ability to function, Hale housed them in wells dug beneath the two towers. This not only provided a constant temperature but also gave the large spectrographs sufficient room to operate properly.

Solar observation was not the only role of Mount Wilson Observatory, however. The success of the 40-inch telescope at Lake Geneva inspired Hale to build a 60-inch (152-centimeter) telescope at Mount Wilson. This telescope was built for its value in observation and to test designs for the building of a 100-inch (254-centimeter) telescope, Hooker telescope the largest of its day. In 1906, Los Angeles businessman John Daggett Hooker Hooker, John Daggett provided the funds to build an 84-inch (213-centimeter) telescope. A short time later, Hooker increased his funding so the 100-inch telescope could be built. During a visit to Mount Wilson in 1910, Andrew Carnegie Carnegie, Andrew announced that he would provide half a million dollars to enable the observatory to mount and house the telescope. With adequate funding and the 60-inch telescope complete, Hale began construction of the 100-inch telescope.

Using a modification of the design of the 60-inch telescope housing, Hale was able to construct the building that would house the larger telescope. In fact, the building of the 100-inch telescope was rather uneventful except for the most critical aspect: the telescope’s glass mirror. The glass that was to be used for the mirror was poured in France and imported. No one inspected the glass after it was poured and before it was shipped to the United States, and when it arrived at Mount Wilson, Hale and his colleagues were shocked and disappointed, not because the glass was made from green wine bottles but because it was full of bubbles. Hale was afraid that the bubbles would cause the glass to warp or crack when it expanded and shrank as the temperature changed. The group did not have many options, however, so they decided to take a chance with the glass and proceeded with the grinding and coating required to create the mirror. The bubbles turned out to be harmless, and the construction of the telescope was completed without incident.


Hale’s innovative designs for solar telescopes, coupled with the introduction of attached spectrographs, provided the foundation for intense solar research. There was now available a means to observe solar flares, solar storms, and other solar disturbances as well as a method to understand the internal chemical changes that occur with and precipitate these disturbances.

The 100-inch telescope provided scientists with a view 200,000 times greater than the capability of the human eye. This great power of sight was soon exploited by astronomer Edwin Powell Hubble. At the time the 100-inch telescope was completed, there was controversy among astronomers about the nature of the Milky Way galaxy: Galaxies What were the “clouds” that could be seen in the Milky Way? Using the 100-inch telescope, Hubble discovered that these clouds are actually distant galaxies and that hundreds of galaxies exist that the naked eye had not previously observed. Furthermore, Hubble analyzed the light spectra of these galaxies and discovered that the galaxies were traveling away from the Milky Way. After carefully analyzing the data, he determined that the galaxies farther away were traveling at a greater speed than those closer to the Milky Way. This was the first hard evidence for what would become known as the big bang theory. Big bang theory With the data collected using the 100-inch telescope, scientists were able to determine stellar distances, observe Doppler shifts in the light spectrum, and discover new galaxies.

The success of this telescope and the success of Mount Wilson as the premier site from which to observe inspired Hale to build a larger telescope. He soon discovered that the 100-inch telescope provided information that provoked questions that could be answered only by a deeper look into space. In addition, he had proved that large telescopes could be built successfully and that the increased cost of construction was rewarded with an equivalent increase in scientific data. Because of this success, Hale began work on a 200-inch (508-centimeter) telescope in Palomar, California.

The location of Mount Wilson had as much to do with the success of the observatory there as did Hale’s genius and the sophistication of the instruments, and the location attracted other astronomers throughout the years. The first infrared interferometer research was conducted at Mount Wilson because of its ideal location. Using two telescopes to observe the same star, the interferometer gives scientists a look at the physical changes a star undergoes as it burns out.

Although land-based telescopes have become increasingly sophisticated and are now joined by space telescopes—such as the Hubble, the Compton, the Chandra, and the Spitzer, which capture data in the nonvisible ranges of the electromagnetic spectrum—in the twenty-first century the Mount Wilson Observatory continues to host several of the most technologically advanced facilities in the world for studying astronomical objects. The 100-inch telescope there remains in active service, and the solar towers collect data daily, adding to the world’s longest continuous record of the Sun. Mount Wilson Observatory
Solar astronomy

Further Reading

  • Bracher, Katherine. “Fifty Years Ago: The 200-Inch Hale Telescope on Mount Palomar.” Mercury 27, no. 5 (September 1, 1998). A brief discussion of the importance of Hale’s 200-inch Palomar telescope, written on the occasion of the telescope’s fiftieth anniversary.
  • Brunier, Serge, and Anne-Marie Lagrange. Great Observatories of the World. Richmond Hill, Ont.: Firefly Books, 2005. Oversize volume presents profiles of thirty-six of the world’s leading observatories (including Mount Wilson), ten space-based telescopes, and eleven “observatories of the future.” Focuses on telescope technology. The many illustrations include photographs of the observatories themselves as well as of the celestial objects seen through their telescopes.
  • Florence, Ronald. The Perfect Machine: Building the Palomar Telescope. New York: HarperPerennial, 1995. Account of the building of the 200-inch telescope at Mount Palomar in Southern California focuses on the incredible engineering and scientific achievement the telescope represented and also places that achievement within the social context of the time.
  • Hale, George Ellery. Signals from the Stars. New York: Charles Scribner’s Sons, 1931. This is Hale’s account of the events that led to the founding of Mount Wilson Observatory and his later involvement in the construction of the Palomar Observatory. Gives an overview of the knowledge gained from the work by the many scientists at Mount Wilson.
  • _______. Ten Years’ Work of a Mountain Observatory. Washington, D.C.: Carnegie Institution of Washington, 1915. Hale wrote this book as a defense of the construction of the 100-inch telescope. He goes into much detail about the advances in scientific knowledge, construction techniques, and methods of observing in the hope of convincing the scientific community of the practicality of the telescope.
  • Macpherson, Hector. Makers of Astronomy. Oxford, England: Clarendon Press, 1933. Written while Hale was still alive and active on the construction of Palomar Observatory, this book places Hale in historical context with the great astronomers. Provides some insight into how Hale’s contemporaries viewed him.
  • Trefil, James S. The Moment of Creation. New York: Charles Scribner’s Sons, 1983. An overview of the origins of the universe focused on the big bang theory. Details Hubble’s work at Mount Wilson and explains the Doppler effect, the expansion of the galaxies, and how stellar distances are measured. Includes illustrations and bibliography.
  • Woodbury, David O. The Glass Giant of Palomar. New York: Dodd, Mead, 1941. An excellent book detailing the creation of Hale’s two giants: the 100- and 200-inch telescopes. Includes a brief biography of Hale, a history of the problems encountered at Mount Wilson, and the history of Palomar Observatory through its completion. Also examines the foundational work done at Mount Wilson. Illustrated, with a bibliography.

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