OUR GALAXY ------------- The position of the Sun in the Milky Way Galaxy is best described as $a) in the disk, slightly more than halfway out from the center b) very close to the center c) in an open cluster in the disk d) in a globular cluster in the halo Trigonometric parallax, the apparent motion of stars due to the Earth's annual motion around the Sun, can be used to study the structure of our galaxy a) within the solar system b) up to about 1 parsec (3.26 light years) from the Sun $c) within about 100 parsecs of the Sun d) within about 100 parsecs of the galactic center The disk of stars that forms the major component of the Milky Way Galaxy has its shape due to a) gas pressure from outside the galaxy $b) rotation combined with self-gravity c) collapse due to self-gravity d) rotation alone e) the cosmological expansion of the Universe The thickness of our galaxy's disk is determined by the a) circular speed of stars around the galaxy b) random motion of stars in the plane of the disk $c) random motion of stars perpendicular to the disk d) the amount of matter in nucleus of the galaxy When we observe stars near the center of the Milky Way Galaxy, we detect light that was emitted from those stars about a) 200 million years ago. $b) 25,000 years ago. c) 8 years ago. d) 8 minutes ago. e) when the galaxy was formed An observer far outside our galaxy would best describe our galaxy and the Sun's position in it as a a) disk of stars centered on our solar system b) disk of stars with a bulge containing our solar system $c) disk of stars with our solar system near the edge d) sphere of stars centered on our solar system e) sphere of stars with our solar system near the edge The mass of our galaxy is best found by a) counting the number of stars in the sky b) counting the star clusters in the sky c) counting the hot, massive main sequence stars d) radio measurements of the amount of interstellar hydrogen $e) measuring the rotation of the Galaxy You could best map out the overall spiral structure of our Galaxy by finding $a) young open clusters and neutral atomic hydrogen gas b) evolved stars like planetary nebulae, RR Lyrae stars c) smooth, round globular clusters d) high velocity stars Choose the best evidence that the disk of the Milky Way Galaxy does NOT rotate like a solid wheel. $a) Disk stars have doppler shifts b) The brightest disk stars form spiral arm shapes c) Disk stars rotate twice as quickly that are twice as far from the Galactic center d) The rotation of disk stars around the Sun decreases with distance according to Kepler's laws Compared to stars like the Sun in the disk of the Milky Way, stars that populate the extended spheroidal halo of the galaxy were born a) earlier, so have had time to accumulate more heavy elements. b) later, so have used up their heavy elements. $c) earlier, from more nearly primordial material, so have fewer heavy elements. d) later, so have accumulated more heavy elements from previous generations of stars. You observe two stars at the same distance. One is in the disk of the Milky Way, the other in a direction perpendicularly out of the disk. Chances are that the disk star will be a) less luminous, have a smaller doppler shift and be reddened by dust b) more luminous, have a smaller doppler shift and be reddened by dust $c) more luminous, have a larger doppler shift and be reddened by dust d) more luminous, have a smaller doppler shift and be less reddened by dust A cold thin cloud of interstellar gas embedded in a hotter, thinner surrounding medium would yield 21-cm radio spectral emission lines of hydrogen showing a) a single broadened emission line. b) broad emission with a narrow spike-like absorption core. c) broad absorption with a narrow spike-like emission core. $d) a narrow spike-like emission core and low broad shoulders of emission. The primary reason that massive O-type stars are not found in the galactic halo is because they are a) too massive to be kicked into the halo from the disk. b) so massive that they settle into the thinner disk. $c) too short-lived to have persisted from halo formation until today. d) closer to us in the disk than in the extended halo. The formation of the Milky Way can be divided into 2 phases: a spherical gas cloud collapsed to form the stars in the Milky Way's spheroid, then rapidly rotating gas collapsed into a disk-shaped configuration of stars. Since disk stars have higher metallicity, which is most likely? Gas ejected from the $a) spheroid stars enriched the material now in the disk stars. b) spheroid stars decreased their metallicity. c) spheroid decreased its angular momentum. d) disk stars puffed out the spheroid stars into a rounder shape.