Ferdinand Ellerman (May 13, 1869 to March 20, 1940) was an American astronomer and photographer. He spent a good part of his career as an associate of the solar astronomer George E. Hale, and is known for his study of a phenomenon in the solar chromosphere later dubbed Ellerman bombs.
Ellerman was hired as an assistant by astronomer George E. Hale in 1892 to observe at his private Kenwood Observatory in Chicago, beginning a working relationship that would last until Hale's death in 1938.[6] The two likely first met during the initial meeting for the Chicago Section of the Astronomical Society of the Pacific, in November 1890, and Ellerman may have first worked as a volunteer for Hale.[7] Ellerman performed much of the observation work for Hale, who focused on travel and organizational activities.[8]: 10–11 On May 16, 1895, Ellerman was married to Hermine Louise Hoenny. They would have one daughter, Louise, who was born July 29, 1901.[2]
During March 1904, Ellerman joined Hale on an expedition to investigate the viewing conditions on Mount Wilson in California. The goal was to determine the suitability for a proposed observatory at the site that was to be financed by the Carnegie Institution. The initial planned instrument was to be the Snow Horizontal Telescope, a solar telescope funded by Helen Snow of Chicago.[13] This instrument was made operational on March 15, 1905, with Ellerman serving as the primary observer on the new spectroheliograph.[14][15] During the early period, Ellerman took a photograph of the Sun in white light nearly every day, then images at a specific wavelength.[7] His skills at repair and jury-rigging equipment proved invaluable at the remote mountain site. A fully-equipped machine shop was soon added to the Observatory for Ellerman's use. Much of the subsequent growth of the Mount Wilson Observatory was documented by Ellerman's photography.[16]
Ellerman's work with Hale resulted in the discovery of solar vortices, which in turn led to the identification of the magnetic fieldsofSun spots in 1908. Later work discerned the polarity of Sun spots, which led to the discovery of the reversal of the magnetic field in these features.[3][17] In 1910, Ellerman was granted a leave from the Carnegie Institution to undergo a one-man expedition to the Hawaiian Islands for the observation of Halley's Comet during its passage.[18] Arriving on March 28, his observation station was set up on Diamond Head, Hawaii. He first sighted the comet on April 14, and by the 25th he was able to take observations. Despite clouds and windy conditions, he took a total of 73 photographs of the comet on 36 different dates.[19][20]
Sunspot illustration by Ellerman, 1917
While at the Mount Wilson Solar Observatory in 1915, Ellerman studied an unusual phenomenon observed at multiple locations in the lower chromosphere layer of the Sun. These events showed bright emission features in the wings of hydrogen-alphaabsorption lines.[21] The phenomenon later became referred to as Ellerman bombs, as he observed they were localized and generally only lasted 10–20 minutes.[22] Although Ellerman studied this phenomenon, the original discovery of this behavior was made by W. M. Mitchell in 1900, near an active region of the Sun.[23]
Ellerman received an honorary MS degree from Occidental College on June 20, 1927.[24] During the spring of 1929, Ellerman accompanied E. Hubble and M. L. Humason in a series of trips to find a suitable location for the proposed Hale Telescope. These journeys were made to a hilly region to the south of Los Angeles and to Arizona, with the goal of checking the viewing conditions. Ellerman served as the mechanic for the trip, setting up the small telescopes.[25] His reports would heavily influence the selection of the final site for the telescope.[16]
^ abAhn, Eun-Joo (2022), "Finding the Invisible Workers in Astronomy: The Case of Mount Wilson Observatory, 1900–1930", Historical Studies in the Natural Sciences, 52 (5): 555–588, doi:10.1525/hsns.2022.52.5.555.
^Hale, George E.; Ellerman, Ferdinand (1903), "The Rumford spectroheliograph of the Yerkes Observatory", Publications of the Yerkes Observatory, 3: I.1–XV.2, Bibcode:1903PYerO...3....1H.
^Hale, George E.; et al. (1904), "The Spectra of Stars of Secchi's Fourth Type", Publications of the Yerkes Observatory, 2: 253–385.8, Bibcode:1904PYerO...2..253H.
^Hale, George Ellery (1900), "Observations of the total solar eclipse of May 28, 1900, at Wadesboro, N. C", Bulletin of the Yerkes Observatory of the University of Chicago, 14, University of Chicago Press: 81–89, Bibcode:1900YerOB..14...81H.
^Adams, Walter S. (December 1954), "The Founding of the Mount Wilson Observatory", Publications of the Astronomical Society of the Pacific, 66 (393): 267, Bibcode:1954PASP...66..267A, doi:10.1086/126721.
^Hale, George E.; Ellerman, Ferdinand (1906), "No. 7. The five-foot spectroheliograph of the solar observatory", Contributions from the Mount Wilson Observatory, 7, Carnegie Institution of Washington: 1–10, Bibcode:1906CMWCI...7....1H.
^Hale, G. E.; et al. (1918), "No. 148. The general magnetic field of the Sun. Apparent variation of the field-strength with level in the solar atmosphere.", Contributions from the Mount Wilson Observatory, 148, Carnegie Institution of Washington: 1–49, Bibcode:1918CMWCI.148....1H.
^Ellerman, Ferdinand (August 1910), "An Expedition to Photograph a Comet", Publications of the Astronomical Society of the Pacific, 22 (133): 165, Bibcode:1910PASP...22..165E, doi:10.1086/122010.
^Ellerman, Ferdinand (1917), "No. 141. Solar hydrogen "bombs"", Contributions from the Mount Wilson Observatory, 141, Carnegie Institution of Washington: 1–3, Bibcode:1917CMWCI.141....1E.
