Pettit, Edison, 1889-1962

Edison Pettit was an astronomer on the staff of the Mount Wilson and Palomar Observatories for thirty-five years. An observer and instrumentalist, he was a pioneer in the early fields of infrared and ultraviolet research. His main interest was in the sun but later expanded to include the moon and planets. His collaboration with Seth B. Nicholson on the heat radiation from the planets and moon was the most significant research on these bodies during the first half of the twentieth century. Edison Pettit was born in Peru, Nebraska on September 22, 1890. His interest in science grew after he entered the Peru State Normal School where he became the student assistant in the physical laboratory in 1904. One year later he began working in the small observatory at the school. From 1906 to 1907, Pettit was out of school, working at the electric light plant which his father helped organize. Although not in school, Pettit gained a great deal of practical experience. He returned to Normal School and graduated in 1910, but stayed on an extra year and graduated with the first college class at Peru in 1911. After graduation, Pettit obtained a job as a science teacher at Minden, Nebraska, High School until 1914. In 1914, he became instructor in physics and astronomy at Washburn College in Topeka, Kansas. The college had an observatory with an 11-inch refracting telescope and Pettit would use this instrument to observe double stars, comets, and Jupiter. While at Washburn, Pettit would occasionally spend summers at the Yerkes Observatory of the University of Chicago. His growing connection with the staff at Yerkes prompted Pettit to leave Washburn College in 1918 and become a graduate student at the University of Chicago. As a graduate student in astronomy, Pettit was assigned as a student assistant at Yerkes Observatory in Williams Bay, Wisconsin. His chief work at Yerkes centered on the study of solar prominences. During the solar eclipse of June 8, 1918, Pettit was stationed at Matheson, Colorado, and used the 11-inch objective from Washburn College Observatory to photograph the corona. That same year, Pettit met and married another astronomy graduate student at Chicago, Hannah Steele. On May 29, 1919, Pettit observed an incredibly large prominence and was able to follow it through its course. He was able to develop a formula describing the development of the prominence and used this as the basis of his Ph. D. thesis, "The Forms and Motions of Solar Prominences," which was completed in 1920.

During his stay at Yerkes, Pettit came to the attention of the director of the Mount Wilson Observatory, George Ellery Hale. Hale, the former director of Yerkes, offered Pettit a position at Mount Wilson. Hannah Pettit, who obtained her Ph. D. in 1919, was given a job as a computer at Mount Wilson. Shortly after his arrival, Pettit was assigned the task of constructing vacuum thermocouples in order to measure radiation from stars and planets. This work, done in collaboration with Seth Nicholson, was in response to the effort mounted at Lowell Observatory by William W. Coblentz and Carl O. Lampland. After six months, Pettit became adept at constructing the tiny thermocouples and the Mount Wilson astronomers soon caught up with the Lowell workers. Together, Pettit and Nicholson measured the radiation from all types of stars, obtaining their temperatures, diameters, and established the concept of radiometric magnitudes. Using the same instruments, they also calculated the surface temperatures of the planets and the moon. Pettit measured the temperature of the moon during a lunar eclipse, obtaining the rate of cooling and heating by the sun. These data were then used to determine the lunar heat capacity and conductivity. The results of this work were generally confirmed by the Lowell researchers and were quickly accepted by astronomers. The work remained as the basis for all stellar and planetary temperature measurements until the 1960s, when new methods, including planetary fly-bys, replaced the older results. Another field in which Pettit specialized at Mount Wilson was the study of ultraviolet solar radiation. Using thermopiles, Pettit attempted, beginning in 1924, to study the variability of the solar ultraviolet and at first believed he had found evidence of large variability. After more research, however, it was concluded that the variability was caused by changes in the amount of ozone in the earth's atmosphere and not by changes in solar energy output. The Mount Wilson work was supplemented by occasional trips, beginning in 1930, by Pettit to the Carnegie Institution of Washington's Desert Laboratory in Tucson, Arizona. Pettit's ultraviolet work was of great interest to the medical community as ultraviolet light was being considered as a treatment for tuberculosis and other diseases.

Pettit's interest in solar prominences continued at Mount Wilson Observatory. Combining his research there with summer trips to Yerkes or the McMath-Hulbert Observatory in Michigan, Pettit eventually published a catalog of all well-observed eruptive prominences. He also started using 16-millimeter motion picture cameras attached to telescopes to photograph solar prominences. These movies were an excellent tool for the study of prominences and were popular items at astronomical gatherings. Among other work that Pettit indulged in was providing consultation to the researchers at the Desert Sanatorium of Southern Arizona and providing materials for the North American Almanac. Pettit retired from the Mount Wilson and Palomar Observatories in 1955. He stayed at his Pasadena home, working in his private machine shop and observing with the 6-inch Clark refracting telescope that he purchased in Michigan. Much of his time was spent in visiting his wife in the hospital, after she had suffered a severe stroke. In 1961, Hannah Steele Pettit passed away and shortly thereafter, in January, 1962, Pettit suffered a stroke. He was forced to move to Tucson to stay with one of his two daughters, Marjorie Pettit Meinel. Not too long after that, however, he suffered a second stroke and passed away on May 5, 1962.

From the description of Papers of Edison Pettit, 1920-1969. (Huntington Library, Art Collections & Botanical Gardens). WorldCat record id: 709807680