Vesto Slipher

Vesto Slipher was an American astronomer at Lowell Observatory who carried out the first measurements of the radial velocities, meaning the speed at which an object is moving toward or away from Earth, of what were then called spiral nebulae and are now known to be entire separate galaxies. Beginning around 1912, Slipher found that the great majority of these galaxies show their light shifted toward the red end of the spectrum, a redshift indicating they are receding from Earth at very high speed, work that supplied the first empirical observational evidence later used by Edwin Hubble and others to establish that the universe is expanding. In 1914 Slipher also made the first detection of the rotation of a spiral galaxy, measuring different velocities on opposite sides of the Andromeda nebula consistent with the whole structure spinning, and in 1929 he discovered the faint sodium layer present high in Earth's own upper atmosphere. Slipher spent virtually his entire long career at Lowell Observatory, eventually serving as its director, and his painstaking spectroscopic measurements, made with instruments and techniques he had to refine himself for the task, quietly laid essential observational groundwork for the twentieth century transformation in scientific understanding of the scale and behavior of the universe.