US astronomer who established that spiral nebulae lie beyond
our Galaxy. He also discovered the existence of particles of matter
in interstellar space. His work in spectroscopy increased our knowledge
of planetary and nebular rotation, planetary and stellar atmospheres,
and diffuse and spiral nebulae.
Slipher was born in Mulberry, Indiana, attended Indiana University,
and in 1902 joined the Lowell Observatory in Arizona. He was director
of the observatory 1926-52.
Slipher measured the period of rotation for Venus, Mars, Jupiter, Saturn,
and Uranus. His work on Jupiter first showed the existence of bands
in the planet's spectrum, and he and his colleagues were able to identify
the bands as belonging to metallic elements, including iron and copper.
He also showed that the diffuse nebula of the Pleiades had a spectrum
similar to that of the stars surrounding it and concluded that the nebula's
brightness was the result of light reflected from the stars.
Slipher's measurements of the radial velocities of spiral nebulae 1912-25
suggested that they must be external to our Galaxy. This paved the way
for an understanding of the motion of galaxies and for cosmological
theories that explained the expansion of the universe.