About the Observatory

“At nightfall nature invites us to forget for a while the things of earth and to look up to the heavens.”

Robert H. Baker, Observatory Director, 1923-1951


Welcome to the University of Illinois Astronomical Observatory. One of the oldest buildings on campus, students and faculty have been observing the night sky since 1896. Pioneering research on measuring the brightness of stars by the second director Joel Stebbins merited recognition as a National Historic Landmark.

The Observatory has born witness too much of the history of the 20th century.  The second director Joel Stebbins served on the American delegation that help rebuilt the International Astronomical Union in the aftermath of World War I.  The third director, Robert Baker, used a photoelectric cell to help open the 1933 Chicago World’s Fair.  Baker was also a popular author publishing two textbooks and numerous other astronomy books.   The fourth director was Dr. George McVittie. During World War II he worked at the British intelligence center at Bletchley Park where he founded the Meteorological Centre. McVittie along with electrical engineering professor George Swenson and several students built a radio telescope behind the Observatory to detect the signals from the Russian Sputnik satellite in 1957. Comet Halley was seen for the second time from the Observatory in 1986. While the Observatory was constructed as a teaching facility and a witness to the historical events, it also made history.

The University of Illinois Observatory is historically significant for the development of selenium and photoelectric cell photometry that revolutionized the measurement of celestial magnitudes. The determination of stellar magnitudes is one of the most fundamental measurements in astronomy. During the years from 1907 to 1922, Observatory director Joel Stebbins worked with physicists F.C. Brown, W.F. Schulz, and Jakob Kunz to develop and refine electric photometry.

In 1910, Stebbins published a study of the eclipsing binary star Algol using a photometer based on a selenium cell.  This work was the most accurate set of photometric observations up to that time and was the first demonstration of the secondary eclipse, proof of the photometer’s superiority to other methods. Stebbins continued to study eclipsing variable stars and refining the instrument. By 1914, he replaced the selenium cell with a photoelectric cell improving sensitivity. The use of electricity for empirically gathering astronomical data revolutionized astronomy.

As a result of Stebbins' work beginning at Illinois and continuing at the University of Wisconsin, photoelectric photometry became the standard technique for determining stellar magnitudes in the 20th Century. It transformed the measurement of astronomical radiation from imprecise visual and photographic methods, to a quantifiable science.

In 1989, the United States Department of the Interior designated the Observatory and National Historic Landmark.

Although light pollution has made the Observatory unsuitable for research it became the headquarters for the expanding Department of Astronomy. As optical and radio telescopes were constructed off campus, the Observatory provided classroom space, offices, and a location where instruments were developed and data analyzed. By 1956 an addition to the Observatory was added in the southwest corner and in 1966 another addition on the east side supported the growing department. The Astronomy Department moved to a new building in 1979 and since then the Observatory is used primarily for undergraduate astronomy classes. Various other organizations occupy the office space.


Awards and Recognition

"The work of Stebbins at the University of Illinois was directly responsible for the United States being the country of origin of the most practical and most accurate method for measuring the brightness of all kinds of celestial objects. Today, in addition to it use in ground-based observatories, it is the principle method of detection in artificial satellites and in space vehicles such as Voyager 2."

Dr. Gerald Kron, Pinecrest Observatory

"The large telescopes built on mountaintops in the western part of the United States are deservedly cited as landmark development in the history of astronomy that led to epoch-making discoveries. The power of these instruments to reach out to the depths of space depend not only on their size but even more importantly on the sensitivity of the detector that records what they see. The now virtually complete photoelectric revolution is therefore, in my opinion, a development that can indeed be considered a landmark."

Dr. Albert Whitford, Lick Observatory