Andrew McKellar, MBE, FRSC (February 2, 1910 – May 6, 1960) was aCanadianastronomer who first detected the presence of molecular matter in interstellar space, and found the first evidence of the cosmic radiation left over from theBig Bang.
He was born inVancouver, British Columbia, Canada, toScottish parents, one of six children of John H. and Mary Littleson McKellar. He studiedmathematics and physics at theUniversity of British Columbia, graduating in 1930. He began graduate studies at theUniversity of California, being awarded hisM.S. in 1932 and aPh.D. the following year. Applying to theUnited States National Research Council, he was awarded a post-doctoral study program for two years atMIT.
In 1935 he joined theDominion Astrophysical Observatory, where he performed research intoastrophysics. He was married to Mary Crouch (b. June 3, 1911, d. Nov. 30, 2000) in 1938, and the couple bore two children, Andrew Robert William (Bob) (b. March 28, 1945), and Mary Barbara (b. Nov. 1, 1946) (McKellar) Bulman-Fleming. DuringWorld War II he served with theRoyal Canadian Navy, in the Directorate of Operational Research.
In 1940, McKellar made the first identification of molecular matter in theinterstellar medium, identifying the spectrum of the organiccyano radical (CN) and themethylidyne radical (CH).[1] The following year, his analysis of the spectra of the cyano radical showed that the surrounding space was very cold with a temperature of approximately −271 °C. At the time, the significance of this was not appreciated; the distinguished Canadian chemist and future Nobel LaureateGerhard Herzberg said that the temperature measurement "...has of course a very restricted meaning".[2] Almost 25 years laterArno Penzias andRobert Woodrow Wilson detected microwave radiation coming from all regions of the sky corresponding to the same temperature of −271 °C found by McKellar, thus revealing its ubiquity and relation to the radiation left over from theBig Bang. McKellar's early death, after a prolonged illness, in 1960 precluded him from consideration for the Nobel Prize awarded to Penzias and Wilson in 1978.
Following the war, from 1952 until 1953, he was visiting professor at theUniversity of Toronto department of physics. Between 1956 and 1958 he served as president of theAstronomical Society of the Pacific, then in 1959 he became president of theRoyal Astronomical Society of Canada for a year. He continued working at the DAO up until four days before he died inVictoria, British Columbia from complications due to lymphoma contracted during his service in the Navy during the War.
He was noted for his work in molecularspectroscopy. Among his contributions was the first estimation of the temperature of interstellar gas (and thereforedeep space) as 2.4°K based on the excitation of CN doublet lines, and finding evidence for the carbon-nitrogennuclear cycle as the energy source forcarbon stars. (The temperature estimate was subsequently confirmed with the discovery of thecosmic microwave background radiation, which has a measured temperature of 2.725 K.) During his career he was the author (or co-author) of 73 scientific publications.
