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Vesto Melvin Slipher (Template:IPAc-en; 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.<ref name="nytimes1969">Template:Cite news</ref><ref name=wayhunter>Template:Cite book</ref><ref>Template:Cite bookPhysics ArXiv preprint</ref><ref>Template:Cite bookPhysics ArXiv preprint</ref> He was also the first to relate these redshifts to velocity.<ref>Template:Cite journal</ref>
Early life and educationEdit
Vesto Melvin 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.<ref name=":1">Template:Cite journal</ref> Vesto had a younger brother, Earl C. Slipher, who was also an astronomer at Lowell Observatory.<ref name=":1" /> 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.<ref name=":2">Template:Cite journal</ref> Two years later, Slipher earned his Master's Degree in the same program.<ref name=":2" /> At the age of 33, Vesto graduated with his Ph.D. in Mechanics and Astronomy from Indiana University.<ref name=":2" />
CareerEdit
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.<ref name=":3" /> Cogshall convinced Percival Lowell, director of the Lowell Observatory in Flagstaff, Arizona, to take Vesto in as a temporary assistant.<ref name=":3">Template:Cite journal</ref> Slipher worked as an assistant from 1901 to 1915 when Lowell finally named him the assistant director of the observatory.<ref name=":4" /> One year later Percival Lowell died and Vesto became the acting director for the next ten years.<ref name=":4" /> In 1926, 25 years after arriving in Flagstaff, Slipher was named director of the Lowell Observatory.<ref name=":4" /> He remained in charge for 28 more years when he retired from professional life.<ref name=":4">Template:Cite journal</ref> 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 the Solar System's planets' rotation interval.<ref name=":5">Template:Cite book</ref> He was one of the first astronomers to show that Uranus has a much faster rotation than Earth, similar to the other giant planets in the Solar System.<ref name=":5" /> What Vesto is most known for though is his work with spiral nebulae, or, spiral galaxies, like the Milky Way and Andromeda.<ref name=":5" /> His initial goal was to measure how fast the nebulae were moving.<ref name=":5" /> His discoveries were confirmed ten years later when Edwin Hubble used the Mount Wilson Observatory reflector to view the galaxies much more clearly.<ref name=":5" />
DiscoveriesEdit
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.<ref name=":6">Template:Cite book</ref> He found that the planets showed different absorption lines that were not present in sunlight, and identified those bands with ammonia and methane.<ref name=":6" /> 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.<ref>Template:Cite book</ref> 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.<ref>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.</ref> Using the Doppler effect and noting subtle changes, he measured the speeds in which spiral nebulae traveled during his research from 1912 and onward.<ref name=":0">Template:Cite book</ref> These subtle changes in the speeds of the nebulae led Slipher to conclude that the nebulae were not within the Milky Way galaxy.<ref>Template:Cite book</ref> In 1914, Slipher also made the first discovery of the rotation of spiral galaxies.<ref>Template:Cite news</ref> He discovered the sodium layer in 1929.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> He was responsible for hiring Clyde Tombaugh and supervised the work that led to the discovery of Pluto in 1930.<ref name="nytimes1969" />
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.<ref>Template:Cite journal </ref> 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 the Hubble–Lemaître law (formerly named Hubble's law; the IAU Decision of October 2018 recommends the use of a new name<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>), was formulated by Hubble and Humason in 1929 and became the basis for the modern model of the expanding universe.
Personal lifeEdit
Slipher married Emma R. Munger in 1904 in Frankfort, IN. Vesto and Emma had two children together, David Clark and Marcia Frances.<ref name="Graves Hoyt 1980 415">Template:Cite journal</ref>
In 1901, Vesto Slipher moved to Flagstaff, Arizona and began work at Lowell Observatory.<ref name="Graves Hoyt 1980 415"/> 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.<ref name="Graves Hoyt 1980 415"/> He is buried at Citizens Cemetery in Flagstaff.<ref>Template:Cite book</ref><ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>
AwardsEdit
- Member of the American Academy of Arts and Sciences (elected 1909)<ref>{{#invoke:citation/CS1|citation
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- Lalande Prize (1919)<ref name="nytimes1969"/>
- Gold Medal of the Paris Academy of Sciences (1919)<ref name="nytimes1969"/>
- Member of the United States National Academy of Sciences (1921)<ref>{{#invoke:citation/CS1|citation
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- Member of the American Philosophical Society (1921)<ref>{{#invoke:citation/CS1|citation
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- Henry Draper Medal of the National Academy of Sciences (1932)<ref name="nytimes1969"/><ref name=Draper>{{#invoke:citation/CS1|citation
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- Gold Medal of the Royal Astronomical Society (1932)<ref name="nytimes1969"/><ref>{{#invoke:citation/CS1|citation
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- Bruce Medal (1935)<ref>{{#invoke:citation/CS1|citation
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- The crater Slipher on the Moon is named after Earl and Vesto Slipher, as is the crater Slipher on Mars and the asteroid 1766 Slipher, discovered September 7, 1962, by the Indiana Asteroid Program.