Vesto Melvin Slipher (/ˈslaɪfər/; November 11, 1875 – November 8, 1969) was an American astronomer who performed the first measurements of radial velocities for galaxies. He was the first to discover that distant galaxies are redshifted, thus providing the first empirical basis for the expansion of the universe.[1][2][3][4] He was also the first to relate these redshifts to velocity.[5]
Personal life
Vesto Slipher was born in Mulberry, Indiana, to Daniel Clark and Hannah App Slipher. He spent his early years working on his family farm in Mulberry.[6] Vesto had a younger brother, Earl C. Vester, who was also an astronomer at Lowell Observatory.[6]
Slipher went to high school in Frankfort, IN. He then attended Indiana University in Bloomington, IN and earned his Bachelor's Degree in Mechanics and Astronomy in June 1901.[7] Two years later, Slipher earned his Master's Degree in the same program.[7] At the age of 33, Vesto graduated with his Ph.D. in Mechanics and Astronomy from Indiana University.[7]
Slipher married Emma R. Munger in 1904 in Frankfort, IN. Vesto and Emma had two children together, David Clark and Marcia Frances.[8]
In 1901, Vesto Slipher moved to Flagstaff, Arizona and began work at Lowell Observatory.[8] He spent the next 53 years of his life working at Lowell Observatory as an assistant and then the director of the observatory until his retirement in 1954. Slipher lived until age 93 and died in Flagstaff in 1969.[8] He is buried at Citizens Cemetery in Flagstaff.[9]
Career
While at school at Indiana University, Slipher formed a personal bond with one of his professors, William Cogshall. Cogshall was one of the main reasons Slipher became interested in astronomy in the first place.[10] Cogshall convinced Percival Lowell, director of the Lowell Observatory in Flagstaff, AZ, to take Vesto in as a temporary assistant.[10] Slipher worked as an assistant from 1901 to 1915 when Lowell finally named him the assistant director of the observatory.[11] One year later Percival Lowell died and Vesto became the acting director for the next ten years.[11] In 1926, 25 years after arriving in Flagstaff, Slipher was named director of the Lowell Observatory.[11] He remained in charge for 28 more years when he retired from professional life.[11] Slipher spent his years there studying many things, but most notably, spectroscopy and redshifts of spiral nebulae.
The first major task Slipher was given was to measure our solar system's planets' rotation interval.[12] He was one of the first astronomers to show that Uranus has a much faster rotation that Earth, similar to the other gas giants in our solar system.[12] What Vesto is most known for though is his work with spiral nebulae, or, spiral galaxies, like the Milky Way and Andromeda.[12] His initial goal was to measure how fast the nebulae were moving.[12] His discoveries were confirmed ten years later when Edwin Hubble used the Mount Wilson Observatory reflector to view the galaxies much more clearly.[12]
Discoveries
Slipher, sixth from left, at the 1910 Fourth Conference International Union for Cooperation in Solar Research at Mount Wilson Observatory
Slipher introduced as early as 1909 that the infrared spectrum could be recorded using photographic emulsions, and used those to record the absorption lines of sunlight and major planets.[13] He found that the planets showed different absorption lines that were not present in sunlight, and identified those bands with ammonia and methane.[13] In the early twentieth century, Vesto Slipher elongated the spectrum to include the red and infrared wavelengths and showed that the major planets display strong absorption lines at many different wavelengths.[14] Slipher used spectroscopy to investigate the rotation periods of planets and the composition of planetary atmospheres. In 1912, he was the first to observe the shift of spectral lines of galaxies, making him the discoverer of galactic redshifts.[15] Using the Doppler effect and noting subtle changes, he measured the speeds in which spiral nebulae traveled during his research from 1912 and onward.[16]
These subtle changes in the speeds of the nebulae led Slipher to conclude that the nebulae were not within the Milky Way galaxy.[17] In 1914, Slipher also made the first discovery of the rotation of spiral galaxies.[18]
He discovered the sodium layer in 1929.[19] He was responsible for hiring Clyde Tombaugh and supervised the work that led to the discovery of Pluto in 1930.[1]
By 1917, Slipher had measured the radial velocities of 25 "spiral nebulae," and found that all but three of those galaxies were moving away from us, at substantial speeds. Slipher himself speculated that this might be due to the motion of our own galaxy – as in his sample, those galaxies moving towards us and those moving away from us were roughly in opposite directions.[20] In hindsight, this was the first data supporting models of an expanding universe. Later, Slipher's and additional spectroscopic measurements of radial velocities were combined by Edwin Hubble with Hubble's own determinations of galaxy distances, leading Hubble to discover the (at that time, rough) proportionality between galaxies' distances and redshifts, which is today termed Hubble–Lemaître's law (formerly named as Hubble's law, the IAU Decision of October 2018 recommends the use of a new name[21]), was formulated by Hubble and Humason in 1929 and became the basis for the modern model of the expanding universe.
^ abcdef"Nesto (sic) Slipher, 93, Astronomer, Dies". The New York Times. Flagstaff, AZ (published November 10, 1969). November 9, 1969. p. 47. ISSN0362-4331.
^Way, M.J.; D. Hunter, eds. (2013). Origins of the Expanding Universe: 1912–1932. San Francisco: ASP Conference Series 471. Astronomical Society of the Pacific.
^Nussbaumer, Harry (2013). 'Slipher's redshifts as support for de Sitter's model and the discovery of the dynamic universe' In Origins of the Expanding Universe: 1912–1932. Astronomical Society of the Pacific. pp. 25–38.Physics ArXiv preprint
^O'Raifeartaigh, Cormac (2013). The Contribution of V.M. Slipher to the discovery of the expanding universe in 'Origins of the Expanding Universe'. Astronomical Society of the Pacific. pp. 49–62.Physics ArXiv preprint
^Slipher, V.M. (1917). "Radial velocity observations of spiral nebulae". The Observatory. 40: 304–306. Bibcode:1917Obs....40..304S.
^ abGraves Hoyt, William (1980). Crawford Jr., Bryce; McEuen, Caroline K. (eds.). "Vesto Melvin Slipher". Biographical Memoirs of the National Academy of Sciences of the United States of America. 52. National Academy Press: 413.
^ abcGraves Hoyt, William (1980). Crawford Jr., Bryce; McEuen, Caroline K. (eds.). "Vesto Melvin Slipher". Biographical Memoirs of the National Academy of Sciences of the United States of America. 52. National Academy Press: 414.
^ abcGraves Hoyt, William (1980). Crawford Jr., Bryce; McEuen, Caroline K. (eds.). "Vesto Melvin Slipher". Biographical Memoirs of the National Academy of Sciences of the United States of America. 52. National Academy Press: 415.
^Nickell, Duane S. (2021). Scientific Indiana. The History Press. p. 37. ISBN9781467149488.
^ abGraves Hoyt, William (1980). Crawford Jr., Bryce; McEuen, Carolina K. (eds.). "Vesto Melvin Slipher". Biographical Memoirs of the National Academy of Sciences of the United States of America. 52. National Academy Press: 414.
^ abcdGraves Hoyt, William (1980). Crawford Jr., Bryce; McEuen, Caroline K. (eds.). "Vesto Melvin Slipher". Biographical Memoirs of the National Academy of Sciences of the United States of America. 52. National Academy Press: 414–415.
^ abcdeMoore, Patrick (1986). Men of the Stars. Gallery Books. p. 84. ISBN0831758155.
^Slipher first reports on the making the first Doppler measurement on September 17, 1912 in The radial velocity of the Andromeda Nebula in the inaugural volume of the Lowell Observatory Bulletin, pp. 2.56–2.57. In his report Slipher writes: "The magnitude of this velocity, which is the greatest hitherto observed, raises the question whether the velocity-like displacement might not be due to some other cause, but I believe we have at present no other interpretation for it." Three years later, Slipher wrote a review in the journal Popular Astronomy, Vol. 23, pp. 21–24 Spectrographic Observations of Nebulae, in which he states, "The early discovery that the great Andromeda spiral had the quite exceptional velocity of -300 km(/s) showed the means then available, capable of investigating not only the spectra of the spirals but their velocities as well." Slipher reported the velocities for 15 spiral nebula spread across the entire celestial sphere, all but three having observable "positive" (that is recessional) velocities.
