Editing Hubble's law (section)

=== Slipher's observations ===
In 1912, [[Vesto M. Slipher]] measured the first [[Doppler shift]] of a "[[spiral nebula]]" (the obsolete term for spiral galaxies) and soon discovered that almost all such objects were receding from Earth. He did not grasp the cosmological implications of this fact, and indeed at the time it was [[Shapley–Curtis debate|highly controversial]] whether or not these nebulae were "island universes" outside the Milky Way galaxy.<ref>{{cite journal |last=Slipher |first=V. M. |date=1913 |title=The Radial Velocity of the Andromeda Nebula |journal=[[Lowell Observatory Bulletin]] |volume=1 |issue=8 |pages=56–57 |bibcode=1913LowOB...2...56S }}</ref><ref>{{Cite journal |last=Slipher |first=V. M. |date=1915 |title=Spectrographic Observations of Nebulae |journal=[[Popular Astronomy (US magazine)|Popular Astronomy]] |volume=23 |pages=21–24 |bibcode=1915PA.....23...21S }}</ref>