Research and Recognition

In the early days of V.M. Slipher's career, Percival Lowell tasked him with learning to use a newly-aquired Brashear spectrograph* in the study of rotational periods of planets within our solar system, particularly Venus. 

Slipher took great care in learning the use of the spectrograph and initially worked on projects confirming already well-accepted data about the rotations of Mars, Jupiter, and Saturn to ensure his own comfort with the tool. After having taken command of the spectrograph, Slipher set to work on the problem of the rotation of Venus while nearly simultaneously pursuing his own interest in the radial velocity of stars. This study of the stars began to earn him some acclaim in the astronomical community. 

Eventually, Lowell turned his interest to the study of the so-called "spiral nebulae," which we now know as galaxies. At the time, in the early 20th century, it was not clear what these objects were. They were commonly believed to be stars, or small clusters of stars, within our own Milky Way, which were in the process of their early formation. Slipher began studying the Andromeda "nebula" with the intention of recording its spectra, but after much tinkering with the set-up and functionality of the spectroscope, he decided the time was right to attempt to determine its velocity, a feat not yet performed by any astronomer.

In late 1912, Slipher compared the photographic plates from four nights of exposure and, extrapolating spectral shifts as Doppler shifts, determined the velocity to be extraordinarily high - about three times as high as any other known object in the universe. Within the next two years, and in time for the 1914 meeting of the American Astronomical Society, he had measured and calculated the velocities of fifteen spiral nebulae, most of them tending toward red shift, meaning they were moving away from the Milky Way at extraordinary rates. Others were shifting toward the blue end of the spectrum, implying movement toward our home galaxy. This groundbreaking work led to the eventual revelation of the theory of the expanding universe and is the most important work of Slipher's long career. 

• See also letters between Slipher and Edwin Hubble, who is largely credited for the understanding of the expanding universe. 

It should not go without mention, however, that Slipher was instrumental in the discovery of Pluto in 1930. It was through his careful direction of the observatory after Lowell's death that funding was secured for the renewed search for "Planet X" and a young man named Clyde Tombaugh, an untrained but enthusiastic backyard astronomer, was hired as telescope operator. Tombaugh took and compared the two photographic plates on which he spotted a tiny and faint speck of light that turned out to be Pluto. The work would not have been possible without Slipher's enthusiasm and perseverance.

*An instrument designed to split the spectrum of incoming light into wavelengths, thus identifying the chemical properties of gases and matter, and which records photographic images thereof.