Today in the history of astronomy, a major figure in our understanding of the expanding universe is born.
VM Slifer stands with the Brashear spectrograph, mounted on the 24-inch Clark Telescope, with which he made many of his spectroscopic discoveries – including the observation of numerous spiral nebulae, most of which were moving away from Earth at great speed, indicating the expansion of the universe. Credit: Lowell Observatory Archives
- Weston Melvin Slipper began his 53-year career at Lowell Observatory in 1901, progressing from a staff astronomer to director by 1926, a role he maintained until his retirement in 1954.
- In 1912, Slipper successfully measured the radial velocity of the “Andromeda Nebula”, determining that it was approaching Earth at an unprecedented speed of 300 kilometers per second.
- By 1914, his observations expanded to 15 “spiral nebulae”, showing that almost all displayed high recessional velocities, thereby establishing the empirical basis for an expanding universe.
- Slifer’s velocity measurements were a key component of Edwin Hubble’s 1929 derivation of the velocity–distance relation for galaxies, which collectively advanced the understanding of cosmic expansion, galactic nature, and extragalactic distances.
Westo Melvin Slipper was born on November 11, 1875, on a farm in Mulberry, Indiana. He graduated from high school, taught for a while in a country school, and then enrolled at Indiana University in Bloomington. In 1901, one of Slipper’s professors, Wilbur Coggshall, persuaded the founder of the fledgling Lowell Observatory to bring the young astronomer on the staff. Percival Lowell was reluctant; As far as they are concerned, the association will be temporary. However, in the end, Slifer would remain at the observatory for 53 years. In 1915, he became assistant director, and when Lowell died the following year, Slifer became acting director and then director until 1926. He served as the head of the observatory until his retirement in 1954 at the age of 79.
In the fall of 1912, Slifer recorded a plate of the “Andromeda Nebula” which he felt was good enough to obtain its radial velocity. At that time no radial velocity of nebulae was known. He recorded better plates in November and December 1912, and measured plates in the first half of January, which showed that the nebula was moving three times faster than any previously known object in the universe. On February 3, 1913, he wrote to Lowell that the Andromeda Nebula was approaching Earth at an unheard-of velocity of 186 miles per second (300 kilometers per second), still an accurate value. Lowell wrote, “It seems as if you have made a great discovery.” “Try some other spiral nebulae for confirmation.”
By the 1914 American Astronomical Society meeting, Slifer was able to announce the results of 15 spirals. Almost all were retreating at high speed. Three years later, Dutch astronomer Willem de Sitter theorized that the universe was expanding. It was Slifer’s observations of so-called spiral nebulae that established this fact. And then the nature of galaxies was discovered by Hubble in 1923. By 1929, Hubble obtained his important velocity-distance relationship for galaxies, as Hubble wrote Slifer, “Your velocities and my distances.” Together, Slifer and Hubble uncovered the expanding universe, the nature of galaxies, and a way to measure extragalactic distances.
