Editing Vesto Slipher (section)

==Discoveries==
[[File:Delegates to the Fourth Conference International Union for Cooperation in Solar Research at Mount Wilson Observatory.jpg|left|thumb|upright=1.9|Slipher, sixth from left, at the 1910 Fourth Conference International Union for Cooperation in Solar Research at [[Mount Wilson Observatory]] in [[California]]]]
Slipher introduced as early as 1909 that the [[infrared spectrum]] could be recorded using [[photographic emulsion]]s, and used those to record the absorption lines of sunlight and major planets.<ref name=":6">{{Cite book |url=https://www.worldcat.org/oclc/900836268 |title=A Source Book in Astronomy and Astrophysics, 1900–1975 |date=1979 |publisher=Harvard University Press |others=Owen Gingerich, Kenneth R. Lang |isbn=978-0-674-36667-1 |location=[Erscheinungsort nicht ermittelbar] |pages=67 |oclc=900836268}}</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>{{Cite book |url=https://www.worldcat.org/oclc/900836268 |title=A Source Book in Astronomy and Astrophysics, 1900–1975 |date=1979 |publisher=Harvard University Press |others=Owen Gingerich, Kenneth R. Lang |isbn=978-0-674-36667-1 |location=[Erscheinungsort nicht ermittelbar] |page=117 |oclc=900836268}}</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 [http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1913LowOB...1b..56S&amp;db_key=AST&amp;data_type=HTML&amp;format=&amp;high=448f04e38822894 ''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 [http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1915PA.....23...21S&amp;db_key=AST&amp;data_type=HTML&amp;format=&amp;high=448f04e38822894 ''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">{{Cite book |last=Helicon |url=https://www.worldcat.org/oclc/923353697 |title=Hutchinson Trends in Science : Astronomy. |date=2006 |publisher=Helicon Publishing |isbn=978-1-85986-504-0 |location=Abingdon |pages=15, 19|oclc=923353697}}</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>{{Cite book |last=Publishing |first=Helicon |title=Hutchinson Trends in Science – Astronomy|publisher=Helicon Publishing |year=2006 |isbn=978-1859865040 |pages=15, 19}}</ref> In 1914, Slipher also made the first discovery of the rotation of spiral galaxies.<ref>{{Cite news |last= Slipher |first= Vesto |date=1914 |title= The detection of nebular rotation |journal= Lowell Observatory Bulletin, 62}}</ref>
He discovered the [[sodium layer]] in 1929.<ref>{{Cite web | url=http://www.albany.edu/faculty/rgk/atm101/sodium.htm | title=The Metallic Vapor Layers}}</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>{{cite journal|author=Slipher, Vesto|journal=Proceedings of the American Philosophical Society|volume=56|pages=403–409|year=1917|bibcode=1917PAPhS..56..403S|title=Nebulae}}
</ref>  In hindsight, this was the first data supporting models of an [[Expansion of the universe|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's law|the Hubble–Lemaître law]] (formerly named Hubble's law; the IAU Decision of October 2018 recommends the use of a new name<ref>{{Cite web|url=https://www.iau.org/news/pressreleases/detail/iau1812/|title=International Astronomical Union {{!}} IAU|website=www.iau.org|access-date=2019-08-26}}</ref>), was formulated by Hubble and Humason in 1929 and became the basis for the modern model of the [[expanding universe]].