Q&A Hero

Science

Q: Describe the cycle of life and death we observe in the spiral arms.
Q: Why are the halo stars distributed spherically instead of throughout the disk?
Q: Give the dimensions and shape of the Galactic disk.
Q: Compare the way an optical and radio astronomer would map the Galaxy.
Q: Contrast the open vs. globular clusters in terms of age, color, galactic distribution, chemical composition, and populations.
Q: The Copernican Principle notes that we are nothing special, not at the center of anything. Apply it to the work of Harlow Shapley.
Q: How old is the Galaxy? How do we know this?
Q: Why do we believe a black hole lies toward Sagittarius?
Q: Why is visible light a bad choice for studying the core of the Galaxy? What is better?
Q: The rotation curve of the outer portions of the Galaxy revealed what about its mass?
Q: Contrast the observed visible mass of the Galaxy with its suspected total. Explain the difference.
Q: Compare the rotation of the stars and the spiral density wave pattern in our Galaxy. How is it observed?
Q: What do the orbits of Populations I and II stars tell us about the formation of the Milky Way?
Q: How does metal content vary between young disk stars and older halo stars? Why?
Q: Of what is the galactic halo composed?
Q: The star Arcturus shows a large proper motion, almost perpendicular to the galactic plane. What Population might we assume it belongs to, and why?
Q: If the Galactic Year is defined as the orbital period of the solar system, how long does it take us to circle the center? How do we know?
Q: Why aren't there young stars in the halo?
Q: Compare the orbital motion of stars in the Galactic disk with those in the halo.
Q: What advantage do radio astronomers have over optical ones in mapping the entire Milky Way?
Q: How did Herschel try to map our Galaxy 200 years ago, and why did he fail?
Q: Why were globular clusters so vital to Harlow Shapley's success?
Q: Who discovered the period-luminosity relationship, and why was it so critical?
Q: Why did Hubble have to rely on Cepheids to find the distance to M31, unlike Shapley's use of RR Lyrae stars with the Milky Way?
Q: Describe our location in the Milky Way.
Q: What are the three main parts of our Galaxy?
Q: Sagittarius A* was first noted due to its strong ________ emissions.
Q: The strange object ________ is believed to be the black hole in the center of our Galaxy.
Q: The bending of distant starlight by a closer object, resulting in a temporary brightening of the star, is called ________.
Q: Most of the mass of the Galaxy lies in the ________.
Q: Counting only the material between us and the galactic Center, we measure a mass of ________ billion Suns.
Q: We can estimate the mass of the Galaxy from observations of its ________ curve.
Q: To the outer edge of the Galaxy, the rotation curve finds objects moving ________ than Kepler's Laws would lead us to expect.
Q: According to its rotation curve, the majority of our Galaxy's mass is ________.
Q: Most of the hot, young blue stars lie in the ________ of our Galaxy.
Q: It is the distribution of ________ atoms in the spiral arms that is measured with 21-cm radio maps.
Q: The ________ is the spherical outer portion of the Galaxy, including the orbits of the globular clusters and most dark matter.
Q: According to the ages of the globular clusters, our Galaxy is about ________ times as old as the solar system.
Q: The distribution of Population II stars and globular clusters shows the Galaxy was more ________ in shape when it formed than it is now.
Q: The Galactic Disk has been flattened by the ________ of the Galaxy.
Q: The age of the whole Galaxy has been found from studies of its oldest stars in the ________ clusters that orbit in the Halo.
Q: The distribution of stars in the Galactic Bulge reminds us of the distribution of objects in the solar system's ________ Belt beyond Neptune.
Q: The spherical distribution of the globular clusters in the Halo reminds us of the similar distribution of cometary nuclei in the ________ cloud.
Q: With respect to heavy elements, the stars of the Halo are ________ in metals.
Q: Harlow Shapley found the visible disk of the Galaxy is about ________ kpc across.
Q: The spiral arms are made of bright stars belonging to Population ________.
Q: The three main components of the Milky Way galaxy are the ________, ________, and ________.
Q: Virtually the entire disk of the Galaxy has been mapped using the ________ wavelength.
Q: Almost all the stars we see around us with the naked eye are relatively ________ in age.
Q: Our solar system lies in the galaxy's ________, about 30,000 light years from the Galactic Center.
Q: Open clusters are found in the ________ of our Milky Way Galaxy.
Q: Harvard woman astronomer ________ discovered the period-luminosity relation.
Q: William Herschel's attempt to map our Galaxy was based on ________ in different directions in space.
Q: If our Sun belonged to Population II, it is unlikely that ________ planets could orbit it.
Q: The presence of ________ planets orbiting it shows us the Sun belongs to Population I.
Q: The ________ variables in the closer globular clusters were used by Harlow Shapley to find their distances.
Q: This diagram shows the period-luminosity relationship. A Cepheid variable with a period of 5 days will have a luminosity of ________ solar luminosities.
Q: It was ________ in the Galactic disk that threw Herschel's model of the size and structure of the Galaxy off badly.
Q: Variable stars are ones whose ________ changes over time.
Q: Star ________ have been vital in understanding stellar evolution, finding distances, and mapping the structure of our Galaxy.
Q: Optically mapping the Milky Way is made very difficult because of ________ in the disk.
Q: Both RR Lyrae and Cepheid variables are giants that ________ in size over time.
Q: Edwin Hubble first found the distance to M31 in Andromeda with its ________ variable stars in its spiral arms.
Q: To determine the distance to a Cepheid, we must measure its ________ of pulsation.
Q: Herschel's map of the Galaxy was too small because ________ blocked much of the starlight.
Q: Based on his star counts, Herschel placed the Sun in the ________ of our Galaxy.
Q: All globular cluster stars belong to Population ________.
Q: The center of the Milky Way lies in the direction of the constellation ________.
Q: The nearest comparable galaxy to our own lies in the constellation of ________.
Q: The radio source ________ is located in a place consistent with the center of our Galaxy. A) Cygnus X-1 B) 3C 273 C) 47 Tucanae D) M8, the Lagoon Nebula E) Sgr A*
Q: At the center of our Galaxy lies A) an intensely bright visible superstar. B) a black hole of millions of solar masses. C) a huge emission nebula. D) the largest of all globular clusters. E) a quasar.
Q: Most of the mass of the Milky Way seems to exist in the form of A) population I stars in the disk. B) population II stars in the Halo. C) hydrogen gas in the disk and spiral arms. D) dark matter out in the Halo. E) the black hole in the Galactic Center.
Q: Which method relies on the mass of a dark object revealing its presence? A) asteroidal occultations B) ring occultations C) stellar eclipses D) temporary brightening of a distant star by a gravity lens E) pulsars slowing down irregularly
Q: Most of the mass of our Galaxy lies A) between Earth and the Galactic center. B) in the bright spiral arms. C) outside the luminous part of the Milky Way Galaxy. D) at the galactic center. E) within the bulge.
Q: What observations suggest the mass of the Galaxy goes much farther out than its visible disc? A) 21-cm maps of the spiral arms B) the rotation curve of the outermost portions of the disc C) the orbits of the open clusters in the disc D) infrared observations of distant brown dwarfs E) X-ray images of other galaxies' discs from Chandra
Q: The dark halo is now believed to extend at least A) 8 kpc. B) 15,000 light years. C) 15 kpc. D) 100,000 light years. E) 50 kpc.
Q: What two observations allow us to calculate mass of the portion of the Galaxy within the Sun's orbit? A) the Sun's mass and velocity in orbit of the Galactic Center B) the Sun's age and period of the Galactic Year C) the Sun's orbital velocity and its distance from the Galactic Center D) the Sun's mass and its age E) the Sun's composition and luminosity
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.
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