PCS 181 Chapter 2: Unit 2

• School: Ryerson University
• Department: Physics
• Course: PCS 181
• Professor: Margaret Buckby

Document Summary

Light year = ly = distance that light travels in one year. Mega parsec = mpc = 1million pc. Astronomical unit = au = average distance between the earth and sun = 1. 5x1011 m. A galaxy is a large assemblage of stars which orbit a common center all held together by gravity contains from a few thousand to trillions of stars. Nebula = clouds of gas / distant galaxies. Hubble and humason determined the distances and radial velocities of faraway galaxies. All faraway galaxies are redshifted and receding from us. Hubble law: radial velocity of a galaxy is directly proportional to distance; the farther, the faster it"s moving away from us. (cid:3045)= , h0 = hubble parameter, v = velocity of a galaxy. The universe is expanding space itself is expanding the raisin bread analogy raising bread dough in the oven expands and carries the raisins with it: space expands carrying the galaxies with it.