One Shift, Two Shift, Redshift, Blueshift

By Lauren Amundson

Lowell Observatory astronomer V.M. Slipher is best known for his discovery of the radial velocities of spiral nebulae, which we now know to be galaxies. In 1912, Slipher determined that the spiral nebulae were moving at approximately three times the speed of any other known object. Objects that are moving away from us exhibit a change in wavelength called redshift, and objects moving toward us exhibit blueshift. (What are Redshift and Blueshift?)

Slipher’s discovery laid the groundwork for Edwin Hubble’s research on the expanding universe. We’ve recently digitized our collection of letters between Slipher and Hubble, dating from 1922 to 1953. The two astronomers discuss the rotation and velocities of spiral nebulae, spectrographic images, manuscript drafts, meetings and committees, lectures, and personal topics. You can find the collection here.