Q&A Hero

Q: Density waves may explain A) the lack of blue stars in the halo. B) the random orbits of halo stars. C) the density of red stars in the bulge. D) the spiral arm structure of the Galaxy. E) the large number of open clusters in the halo.

Q: What use are 21-cm radio waves to galactic astronomers? A) They cut through the dusty cocoons to let us watch star birth. B) We can reflect them off the core of the Galaxy. C) Their Doppler shifts let us map the motions and locations of gas in the spiral arms. D) They bounce off stars like our Sun to let us precisely measure their distances. E) They pick up the cool, dark matter much better than can optical telescopes.

Q: Most of the new star formation in the Galaxy is found in the A) halo. B) spiral arms. C) bulge. D) galactic center. E) globular clusters.

Q: The visible color of the Galactic Bulge is A) blue from the OB associations. B) yellow from the old Population II stars. C) red from the emission nebulae. D) black from the dust clouds. E) brown from the dwarfs in the dark matter.

Q: Which sequence of formation is most likely to be correct, oldest to youngest? A) halo, spiral arms, globular clusters B) globular clusters, open clusters, OB associations C) planetary nebulae, Population I stars, population II stars D) Population I stars, population II stars, population III stars E) emission nebulae, planetary nebulae, dark nebulae

Q: In the formation of our Galaxy, the ________ formed first. A) galactic disk B) galactic center C) globular clusters D) planetary nebulae E) spiral arms

Q: Which of these is not typical of the Galaxy's spiral arms? A) hot, young blue Population I stars B) emission nebulae like M42 C) O and B stars D) open clusters E) Population II giants like orange Arcturus

Q: In our location in the Milky Way, the galactic disk is only about ________ ly thick. A) 10 B) 100 C) 1,000 D) 10,000 E) 100,000

Q: The tidal streams mapped in the Halo are similar to ________ in our solar system. A) the asteroid belt between Mars and Jupiter B) meteor swarms in old comet orbits C) the rings around the jovians D) the moons orbiting planets E) the solar wind

Q: Between us and the Galactic Center, the Milky Way has a mass of A) several hundred thousand Suns. B) one to two million Suns. C) 250 million Suns. D) 100 billion Suns. E) over a trillion Suns.

Q: Which of these objects have not been found in the Galactic Halo? A) RR Lyrae variables B) Cepheid variables C) emission nebulae D) Population II stars E) globular clusters

Q: Detailed measurements of the disk and central bulge region of our Galaxy suggest our Milky Way is a A) normal spiral galaxy. B) barred spiral galaxy. C) very flat elliptical galaxy. D) very dusty irregular galaxy. E) quasar.

Q: What is true about the stellar populations in the Galaxy? A) Only old stars are found in the halo. B) The main star forming regions are outside the Galactic plane. C) The bluest stars are in the halo. D) Red stars are only found in the bulge. E) Most open clusters are in the halo.

Q: The Galactic Year is the time for our solar system to orbit the Galaxy; it is about A) 15 million years. B) 225 million years. C) 4.5 billion years. D) 9.6 billion years. E) 13.5 billion years.

Q: From the Sun, the distance to the Galactic Center is about A) 8,000 light years. B) 8 kpc. C) 100,000 light years. D) 225 million light years. E) 100 billion parsecs.

Q: Galactic disks appear blue because A) they contain no G, K, or M dwarfs. B) they contain only blue reflection nebulae. C) dust obscures the longer, red, wavelengths. D) O and B blue giants are much brighter than G, K, or M dwarfs. E) dark matter gravitationally shifts all wavelengths towards the blue.

Q: The orbits of Population II stars have been compared to A) planets around the Sun. B) satellites around planets. C) comets around the Sun. D) binary stars. E) the accretion disc around a black hole.

Q: Which statement about Population II is false? A) They are made of almost nothing but hydrogen and helium. B) Their orbits around the Galaxy resemble those of comets. C) They formed first as the Galaxy formed. D) At almost five billion years old, our Sun must belong to this older Population. E) The globular clusters are their most obvious groupings.

Q: Which statement is true? A) Our Sun is a Population II star. B) The bright blue stars that dominate the sky are Population I stars. C) Population I stars lie outside the galactic disc. D) Population I stars are the brightest stars in the globular clusters. E) Population II stars probably have terrestrial planets around them.

Q: Harlow Shapley found the Milky Way was A) centered on the Earth. B) much smaller than previously thought. C) rapidly expanding. D) much larger than previously thought. E) uniformly spherical in shape.

Q: What is one of the differences between Cepheids and RR Lyrae variables? A) Cepheids are giants, but RR Lyrae stars are still on the main sequence. B) All Cepheids have the same brightness, but RR Lyrae stars vary greatly in luminosity. C) The period-luminosity relation holds only for RR Lyrae stars. D) The pulsations of RR Lyrae stars are much less regular than those of Cepheids. E) The RR Lyrae stars have much shorter periods than Cepheids.

Q: The period-luminosity relation is critical in finding distances with A) RR Lyrae stars. B) trigonometric parallaxes. C) spectroscopic parallaxes. D) Cepheid variables. E) pulsars.

Q: Which is the correct description of the Sun's location within the Milky Way? A) at the outer edge of the galactic bulge but in the plane of the disc B) in the disc but at its outer edge C) as Herschel found, very close to the Galactic center D) above the disc and about one-third of the galactic radius from the center E) in the disc and about one-half a galactic radius from the center

Q: The location of the Galactic Center was first found by Harlow Shapley with A) radio emissions from Sagittarius A. B) Cepheids of population I in the spiral arms. C) RR Lyrae variables in the globular clusters. D) planetary nebulae in the open clusters. E) infrared observations of the heat from its accretion disk around the black hole.

Q: Which of these variable stars would be classified as a Cepheid? A) a B supergiant with a period of 0.14 days B) an F giant with a period of 14 years C) a G giant with a period of 14 hours D) a K giant with a period of 14 days E) an M supergiant with a period of 140 days

Q: Which of these variable stars would be classified as a RR Lyrae? A) a K giant with a period of 14 days B) an F giant with a period of 14 hours C) an M giant with a period of 140 days D) a B supergiant with a period of 0.14 days E) a pulsar with a period of 0.14 seconds

Q: Why was Herschel's strategy for mapping our Galaxy flawed? A) His infrared telescopes couldn't penetrate the dust clouds. B) He used globular clusters, lying above the dust in the disc. C) He relied on visual wavelengths, which are obscured by dust. D) He used radio telescopes that didn't give enough resolution. E) He assumed Earth was at the extreme edge of the Galaxy.

Q: For finding the distances to globular clusters, Harlow Shapley used A) eclipsing binaries. B) planetary nebulae. C) Type I supernovae. D) RR Lyrae variables. E) Population I classical Cepheids.

Q: A star in the instability strip of the H-R diagram would A) vary in both temperature and radius. B) explode as a Type I supernova. C) vary in temperature and brightness, but not in radius. D) vary in brightness with an irregular pattern. E) vary in temperature and radius, but not in brightness.

Q: Which of the following are most massive and luminous? A) brown dwarfs B) RR Lyrae variables C) white dwarfs D) T-Tauri variables E) Cepheid variables

Q: The RR Lyrae stars all have periods of A) less than a second. B) several minutes. C) several hours. D) several days. E) several weeks.

Q: The first attempt to map the Galaxy via star counts was done by A) Galileo in 1612. B) William Herschel in the late eighteenth century. C) Edward Barnard with long exposure photos about 1900. D) Harlow Shapley with the RR Lyrae variables in 1920. E) Edwin Hubble with the new 100" Mt. Wilson telescope in the 1930s.

Q: All RR Lyrae stars have about the same A) period of six days. B) distance of 32 light years. C) galactic location and speed. D) luminosity of about 100 Suns. E) locations in the centers of globular star clusters.

Q: In structure, our Milky Way is most similar to A) the Large Magellanic Cloud. B) an upscale version of a globular cluster. C) M31, the Andromeda Galaxy. D) the Orion nebula. E) none of these.

Q: The Sgr A* black hole may contain three million solar masses.

Q: Our surveys of the Galactic Center are better done in infrared than visible light.

Q: The core of the Milky Way, Sagittarius A, is a strong radio source in the sky.

Q: Between us and the Galactic Center lie about 100 billion solar masses.

Q: Most of the mass of our galaxy lies between Earth and the Galactic center.

Q: Dark matter has not been observed at any electromagnetic wavelength.

Q: The majority of the mass of the Milky Way lies farther out than the Sun's orbit.

Q: Most of the dark matter in the Galaxy lies in the disk and galactic center.

Q: The density wave theory attempts to explain why the spiral arm structure persists over a long time.

Q: The spiral arms are sites of continuous new star formation, accounting for their blue color and pink emission nebulae.

Q: Like our solar system, the whole Milky Way is about five billion years old.

Q: The stars of the halo are all old, and those of the disk are all new.

Q: The rotation curve for our Galaxy shows stars beyond the Sun moving slower than expected.

Q: It would be very unlikely to find a massive, young star out in the halo.

Q: Planets are expected to be found orbiting most Population II stars.

Q: The orbits of Population II stars and globular clusters are much like comets, rising high above the galactic plane with eccentric orbits.

Q: The thickness of the Galaxy near the Sun is about 1000 light years.

Q: The two stellar populations are extremes, but, in fact, stars with intermediate properties are common.

Q: Around us in the galactic plane, we find stars of a variety of ages and compositions.

Q: The bright blue stars of Orion's Belt are Population I, while our yellow Sun is population II.

Q: The globular star clusters are the most obvious examples of Population II around us.

Q: Stars within an emission nebula, such as M42, are considered Population I stars.

Q: The orbit of the Solar System around the Galaxy is similar to that of a planet, almost circular and in the galactic plane.

Q: Halo stars are all Population II objects.

Q: Cepheids are good examples of cataclysmic variable stars.

Q: Population I stars came billions of years before Population II stars.

Q: 21-cm radio waves allow us to map the distribution of hydrogen in spiral arms on the opposite side of the Galaxy.

Q: Harlow Shapley mapped the Milky Way using the period-luminosity relationship for RR Lyrae stars.

Q: Shapley found the globular clusters were strongly concentrated toward Sagittarius.

Q: Herschel believed the Milky Way was a disk of stars, while Shapley found the extended halo more like a ball.

Q: Like the RR Lyrae stars, Cepheids are all similar in luminosity, hence their use in measuring stellar distances.

Q: All Cepheid variables discovered so far lie in other galaxies.

Q: All RR Lyrae stars are about 5 times the Sun's luminosity.

Q: It is harder to map the structure of the Milky Way in visible wavelengths than with radio and infrared waves.

Q: The instability strip shows that not all main-sequence stars are, in fact, stable.

Q: RR Lyrae stars pulsate, but with shorter periods and lower luminosities than Cepheids.

Q: The instability strip is above the main sequence on the H-R diagram.

Q: William Herschel made the first map of the Galaxy about 200 years ago.

Q: The problem with visual observations of our Galaxy is the luminous gas haze.

Q: Shapley found that globular clusters are only found in the Galactic bulge.

Q: Shapley found the globular cluster distribution equally concentrated all along the galactic plane.

Q: All Cepheids are giants, but not all giant stars are Cepheid variables.

Q: Shapley's measurements of the distances to open clusters vastly revised our understanding of our position in the Galaxy.

Q: Herschel's original disk model placed us close to the center of the Galaxy.

Q: William Herschel's original model for our Galaxy was based on counting stars.

Q: Because of their greater luminosity, RR Lyrae stars can be used at greater distances than can long-period Cepheids.