Vesto Melvin Slipher Biography

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World of Scientific Discovery on Vesto Melvin Slipher

When Vesto Slipher was born, it was commonly accepted that the universe was composed of a single galaxy. Everything that was visible, whether a star or a mysterious, wispy nebula, was a part of the Milky Way.

This opinion had not altered in the twenty-five years following Slipher's birth. When photographed, some of these nebulas showed a spiral configuration, and Astronomer Percival Lowell (1855-1916) felt certain the spiral clouds were planetary systems that were being formed. He hoped that understanding these spirals would increase the knowledge about the formation of our own solar system. Lowell needed someone to perform the study and, in 1901, he hired Slipher to work at the Lowell Observatory.

The process was a simple one: study the spectrum of the light from the nebulas and measure any Doppler shift present. If the light of the nebula was shifted toward the blue end of the spectrum, it meeant the nebula was moving toward us; if shifted toward the red, it was headed away. This work was very time-consuming: it was necessary to expose each photograph from twenty to forty hours, and the procedure had to be carried out over the course of several nights.

By late 1912 Slipher had photographed the Andromeda nebula four times. Upon examination, the spectrum did not look like that of contracting gases. It appeared more like the light of stars. In addition, the entire nebula was shifted toward the blue end of the spectrum, indicating the entire system was approaching the Earth at a speed of 186 miles (300 km) per second.

By 1914 Slipher had analyzed the light from twelve other spirals. Only two showed a blue shift; the others were red-shifted. The extent of some of the red shifts indicated a recession speed of 683 miles (1,100 km) per second. Astronomers realized that velocities this high implied vast distances; these spirals had to be star systems located outside the Milky Way. By 1925, 39 nebulas had been studied. Only six had blue shifts.

The discovery, that same year, that the Milky Way galaxy was rotating caused a revision in the calculations. Of all the nebulas measured, only two really had blue shifts. In addition, the approach of the Andromeda nebula was revised downward to 31 miles (50 km) per second. Slipher's work provided the foundation upon which other scientists, such as Edwin Powell Hubble, built a new theory of the universe. In just two more years, Belgian astronomer Georges Henri Lemaître would divine just what set all these objects into motion.