Unsung Hero Cold Cases – The Slipher File

 As the Milky Way sets, light from nearby villages and mining towns turns the stream of clouds overhead into a rippling river of fool’s gold. On this night in October of 2013, during the first season of observations of the Dark Energy Survey, we pumped caffeine into our bodies to stay awake, to keep ready for when the conditions would change. Every field we can observe, every galaxy we can capture will make a contribution to the greater measurement of their vast patterns – patterns distorted (or created) by a dark energy.

One hundred years ago, an American astronomer by the name of Vesto Slipher became the first to measure streams of galaxies in our local neighborhood. Slipher used the 24-inch telescope at Lowell Observatory to measure velocities of spiral nebulae (i.e., galaxies), through a method known as “spectroscopy.” Most of the galaxies that Slipher measured are receding from the Milky Way, rather than moving toward it – the first indication of cosmic expansion.

This result laid the groundwork for the definitive discovery of the expanding universe. Unfortunately, Edwin Hubble of Mount Wilson is most often accredited with this finding. Hubble measured distances via Cepheid Variables to distant nebulae and then correlated them with Slipher’s velocity (redshift) data to create the famous distance-velocity plot for his 1929 paper.

Hubble provided no citation of Slipher’s work.

Slipher is the first to measure Doppler Shifts (velocities) of galaxies, to show that spiral galaxies rotate, and to detect that collections of stars and dust are actually nebulae outside our own Milky Way.

Let us remember Vesto Slipher – among modern cosmology’s most influential unsung heroes.

Det. B. Nord