American astronomer Vesto Melvin Slipher was the first to measure the velocities of galaxies using their light spectra. // photo courtesy Lowell Observatory
On September 17, 1912, American astronomer Vesto Melvin Slipher changed the study of the universe when he measured the first velocity of a “spiral nebula” from its light spectrum. As an object moves toward us, its light shifts to shorter, and thus bluer, wavelengths; as it moves away from us, its light shifts to longer, and thus redder, wavelengths. (This “Doppler effect” is also responsible for the change in pitch you hear as an ambulance or train passes you.)
Slipher obtained the spectrum of the Andromeda Nebula — now known as the Andromeda Galaxy (M31) — and from that data, he realized the object was moving toward Earth at about 190 miles (300 kilometers) per second. Many of his colleagues doubted the measurement because it was such a huge value. Still, he continued collecting many more Doppler shift velocities of other “nebulae.” Slipher’s data, combined with additional discoveries over the next two decades, would solidify the notion that the universe is expanding — even though his Andromeda velocity measurement was a bit off of the actual value.
Scientists at
Lowell Observatory in Flagstaff, Arizona, are hosting the “
Origins of the Expanding Universe” conference to celebrate Slipher’s first velocity measurement and other findings that led to the understanding of cosmic expansion. (The meeting is taking place at Lowell because Slipher used the 24-inch telescope there for his observations.) The meeting will converge September 15–17 and bring together astronomers and historians of science. However, the Lowell staff says, “You need not be an astronomer or historian to enjoy this timely and important conference.”
So, if this subject is of interest to you, consider registering to attend the talks, poster presentations, and discussions. (I hear there will be homework, too.)