page_title: Astronomical Observatory (University of Illinois at Urbana–Champaign)
section_title: Stebbins' research
hierarchical_section_title: Astronomical Observatory (University of Illinois at Urbana–Champaign) / History / Stebbins' research
caption_attribution_description: selenium cell photometer mounted on a refractor, 1910, University of Illinois Observatory
context_page_description: The University of Illinois Astronomical Observatory, located at 901 S. Mathews Avenue in Urbana, Illinois, on the campus of the University of Illinois at Urbana–Champaign, was built in 1896, and was designed by Charles A. Gunn. It has been listed on the National Register of Historic Places since November 6, 1986, and on December 20, 1989, was designated a National Historic Landmark.
  Though none of the astronomical instruments are being used for professional research today, the observatory still contains a 12" Brashear refractor. The observatory played a key role in the development of astronomy as it was home to a key innovation in the area of astronomical photometry. The facility has been directed by such noted scientists as Joel Stebbins and Robert Horace Baker.
  Erected at the behest of the Illinois General Assembly, the University of Illinois Observatory became important in the development of astronomy due, in large part, to pioneering research by Dr. Stebbins, from 1907 to 1922. Joel Stebbins left the University of Illinois in 1922 but left behind a legacy of discovery that helped alter the face of modern astronomy.
context_section_description: Before 1907, all magnitude measurements for stars were obtained through visual comparison of relative brightness, a process that was slow and inexact. Later photographic methods would use starlight to make a representation on a photographic plate. Regardless, neither method was adequate for quantitative measurements. The drawback of previous methods of measuring stellar magnitude made the use of electricity for empirically gathering astronomical data revolutionary for the science of astronomy. Joel Stebbins' pioneering research for astronomical photometry took place at the observatory.
  Stebbins arrived as director of the University of Illinois Observatory after he completed his Ph.D. at the University of California, Berkeley in 1903. Once Stebbins arrived fresh from his dissertation completed at Lick Observatory, he began a two-year study of the brightness of 107 binary stars using a Pickering visual photometer. The research, with the assistance of his wife, May Stebbins, investigated the relative brightness on binary stars using visual techniques. In a 1957 speech at the American Astronomical Society, Stebbins recalled the events which led up to the electric cells:
  She (May Stebbins) wrote down the numbers as the observer called them, but after some nights of recording a hundred readings just to get one magnitude, she said it was pretty slow business. I responded that someday we would do all this by electricity. That was a fatal remark. Thereafter she would often prod me with the question, "When are you going to change to electricity?" It happened that within two or three months, the Department of Physics gave an open house, and one of the exhibits was in (the) charge of a young instructor, F.C. Brown. He showed how, when he turned on a lamp to illuminate a selenium cell, a bell would ring, when the lamp was off, the bell would stop. Here was the idea: Why not turn on a star to a cell on a telescope and measure a current?
  Stebbins and Fay C. Brown soon became friends and in time, they had a selenium cell positioned on the 12-inch (300 mm) telescope at the observatory. In the summer of 1907, after several attempts, the two achieved a light curve for Earth's moon and measured the moon's brightness during a lunar eclipse. This marked the first time in America that electricity was used to measure astronomical brightness.  Later Stebbins went further, discovering that by cooling the cell to zero degrees Fahrenheit he would double the cell sensitivity and diminish irregularities in the circuit tenfold, still further, by reducing the size of the cell the irregularities were reduced more.  The pair went on to detect stellar intensity and activity that were previously unrecorded.  In 1909 their observations of Algol detected for the first time the second minimum as well as limb brightening. The coming of Comet Halley in 1910 allowed Stebbins, in May, to use his selenium photometer to study the comet. Two years later Stebbins used the photometer and discovered four stars to be eclipsing binary stars: Beta Aurigae, Spica, Alpha Coronae Borealis and Delta Orionis.
  Although the selenium cell photometer was proving successful, it was difficult to use and not very sensitive. Illinois physics professor Jakob Kunz suggested that Stebbins try a photoelectric cell.  Kunz had been doing experimentation on an improved photoelectric cell which was alkali based. Kunz's cell was the predecessor of the modern day "electric eye." Stebbins left for a sabbatical in Europe in fall of 1912. While he was gone, Kunz and another Illinois physicists W.F. Schulz successfully tested a photoelectric cell photometer at the Observatory.
  Upon his return from sabbatical in August 1913, Stebbins ended his pioneering work with the selenium cell and began working with Kunz on the new photometer. A number of other notable astronomical discoveries occurred at the observatory through the years.  In 1915 Stebbins' object of study became the star involved in Myers' first big discovery at the observatory, Beta Lyrae. He thus began an aggressive research program produce
caption: The selenium cell photometer mounted on the refractor telescope in 1910
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