ASTRON 1101 Lecture Notes - Lecture 34: Parsec, Special Relativity, Vesto Slipher

• School: Ohio State University
• Department: Astronomy
• Course: ASTRON 1101
• Professor: Barbara Ryden

Document Summary

Discussing olbers" paradox, i assumed the universe is static (neither expanding nor contracting) If the universe is expanding, galaxies are moving away from us; their spectra will show a redshift to longer wavelength. If the universe is contracting, galaxies are moving toward us; their spectra will show a blueshift to shorter wavelength. In 1912, vesto slipher began measuring the shift in wavelength of galaxy spectra. (in 1912, they were still called nebulae ) He started with the andromeda galaxy, which turns out to be blueshifted. However, a something happened when slipher looked at more galaxies. By 1923, wavelength shifts were known for 41 galaxies: 36 had redshifts, but only 5 had blueshifts. For comparison, stars in the sun"s neighborhood have equal numbers of redshifts and blueshifts. Typical radial velocities for those stars are about 20 km/s: galaxies at large distances are moving away from the milky way galaxy at surprisingly high speeds.