NORMAL GALAXIES --------------- Most of the hydrogen molecules (two hydrogen atoms bound together) in the universe are found in a) cool stars. $b) cold dense interstellar clouds. c) H II regions of ionized hydrogen. e) space between the galaxies. If one region of the sky shows nearby stars but no distant stars or galaxies, our view is probably blocked by a) nothing, but directed toward a particularly empty region of space. b) an emission nebula of ionized gas. $c) an interstellar gas and dust cloud. d) a concentration of dark matter. The dominant mass component in the Milky Way Galaxy interior to the orbit of the Sun is a) gas and dust contained in giant molecular clouds b) cosmic ray particles c) stars $d) dark matter Compared to the present day Milky Way Galaxy, the Milky Way of 3 billion years ago would have had $a) more gas in the disk b) more stars in the halo c) more metal-rich stars d) no Solar System The most effective technique to find distances to other galaxies is to look at objects in the galaxies for which we know the $a) luminosity b) color c) mass d) orbital velocity about the center of the galaxy e) spectral type You are asked to determine an accurate distance to the Andromeda Galaxy. Choose the best technique below. a) Doppler shift of spectral lines $b) period-luminosity law for Cepheid variable giants in Andromeda c) the Hubble law of recession of galaxies d) trigonometric parallax using Earth's orbit Suppose that the period-luminosity law for giant Cepheid variable stars in the Milky Way leaves an uncertainty of 30% in distance estimates made from the measured variability periods of Cepheid stars. Much more distant Cepheids measured in other galaxies will yield distance uncertainties that a) increase with distance. b) are at most 30%. $c) are at least 30%. d) depend on the galaxy. The Tully-Fisher Method of measuring distances to spiral galaxies is based on a relation between the speed of the galaxy's rotation and its absolute luminosity. The existence of the relation suggests that a) distant galaxies are more luminous, with greater velocities. b) rotations of galaxies generate star formation and therefore light. c) luminosity generates rotation. $d) luminous galaxies have more stars, and therefore more mass. Which of the following is impossible to use in estimating distances to other galaxies; why? a) globular clusters; too large and fuzzy $b) white dwarfs; too dim c) pulsating variable stars; too variable d) supernovae; don't last long enough Which of the following is least easily explainable as a result of interaction between galaxies? a) Some galaxies have long "tails" of stars. b) Rich, regular clusters are dominated by central giant ellipticals. $c) Both spiral and elliptical galaxies are seen at very high redshift. d) Some galaxies seems to be undergoing bursts of star formation. The nuclei of most spiral galaxies appear redder than their spiral arms because of $a) young blue stars in the arms, and old red ones in the nuclei b) emission nebulae and dust in the nuclei c) receding nuclei and advancing spiral arms (Doppler shifts) d) nuclear reactions