AS-102 Final Exam Questions With Complete Solutions

1. We classify galaxies by: - ANSWER how they appear in the sky 2. Stars in elliptical galaxies have velocities that: - ANSWER are oriented in random directions 3. If you measure the average brightness and pulsation period of a Cepheid variable star, you can also determine its: - ANSWER Distance 4. An iron core cannot support a massive main-sequence star because: - ANSWER Iron cannot fuse to make heavier nuclei and produce energy 5. Type I and Type II supernovae are respectively caused by what types of stars? - ANSWER white dwarfs, massive stars 6. The speed of light - ANSWER 300,000 km/s 7. A light-year is a unit commonly used in astronomy as a measure of ______. - ANSWER distance 8. An empirical science is one that is based on: - ANSWER observed data 9. The time it takes a planet to complete one full orbital revolution is commonly know as its _______. - ANSWER period 10. If the Sun is located at one focus of Earth's elliptical orbit, what is at the other focus? - ANSWER Nothing 11. Kepler's second law says that if a planet is in an elliptical orbit around a star, then the planet moves fastest when the planet is: - ANSWER closest to the star 12. The natural tendency of an object to resist changes in motion - ANSWER inertia 13. Which property of an astronaut changes when he/she is standing on the Moon relative to when the astronaut is standing on Earth? - ANSWER weight 14. If the distance between the earth and Sun were cut in half, the gravitational force between these two objects would ____________. - ANSWER increase by 4 15. What is the difference between visible light and X rays? - ANSWER wavelength; x-rays have a shorter wavelength than visible light 16. Why do some stars in the sky appear blue, while others appear red? - ANSWER The blue stars have a greater surface temp than the red stars 17. Star C and Star D have the same luminosity. Star C is twice as far from earth as star D. How the brightness of stars C and D compare? - ANSWER Star D appears 4 times as bright as star C 18. What type of spectrum do most stars produce? - ANSWER an absorption spectrum on top of a blackbody spectrum 19. When astronomers refer to "heavy elements" which elements are they referring to? - ANSWER all elements more massive than helium 20. Suppose a planet is discovered orbiting a star in a highly elliptical orbit. While the planet is close to the star it moves __________, but while it is far away it moves __________. - ANSWER faster; slower 21. What is the cosmological principle? - ANSWER The same rules work everywhere in the universe 22. Kepler's second law says: - ANSWER planets move fastest when they are closest to the sun 23. If a star's parallax is measured using identical telescopes, one on Earth and the other on Jupiter, which planet's telescope would measure the biggest parallax? Explain. - ANSWER Jupiter, because it has the largest semimajor axis 24. We observe neutral hydrogen gas using ___________. - ANSWER 21-cm emission 25. When radiation from an object passes through the interstellar medium: - ANSWER the object appears redder and dimmer 26. Dust in the ISM appears dark in ________ wavelengths and bright in ___________ wavelengths. - ANSWER visible; infrared 27. An HII region signals the presence of: (4 things) - ANSWER newly formed stars, young stars, ionized hydrogen gas, O- and B- type stars 28. In the ISM, molecules survive only in regions with: (3 things) - ANSWER low temperature, high densities, lots of dust 29. An accretion disk forms around a collapsing protostar because infalling material must conserve ________. - ANSWER angular momentum 30. The Hayashi track of a low-mass protostar in the H-R diagram is a path of approximately constant ________. - ANSWER temperature 31. The entire process of star formation is really just an evolving balance between _______ and ________. - ANSWER pressure and gravity 32. What critical event transforms a protostar into a normal main-sequence star? - ANSWER Nuclear fusion begins in the core 33. What factor is most important in determining a star's position on the main sequence and subsequent evolution? - ANSWER Mass 34. A young protostar is more _________ than the sun even though its surface temperature is _______. - ANSWER more luminous; cooler 35. Why are protostars difficult to observe? - ANSWER They occur in dusty regions 36. As a main-sequence star burns its core supply of hydrogen, what happens? - ANSWER Helium builds up as ash in the core 37. A low-mass red giant star's energy comes from _________ burning to ____________ in a shell surrounding its core - ANSWER hydrogen; helium 38. When a spectral type G2 star like the Sun leaves the main sequence its __________ increases and its _____________ decreases. - ANSWER luminosity; surface temperature 39. Helium burns in the core of a horizontal branch star via ________ and produces __________. - ANSWER the triple alpha reaction; carbon 40. Asymptotic giant-branch stars have ______________ luminosities, ______________ radii, and ______________ escape velocities. - ANSWER large; large; small 41. What is a planetary nebula? - ANSWER The ejected envelope of a giant star surrounding the remnant of a star 42. What ionizes the gas in a planetary nebula and makes it visible? - ANSWER Ultraviolet photons emitted by a white dwarf 43. A low-mass main-sequence star's climb up the red giant branch is halted by the beginning of ____________ in the core - ANSWER helium fusion 44. The detection of solar neutrinos confirms that: - ANSWER the Sun's core is powered by proton-proton fusion 45. Brown dwarfs are considered failed stars because: - ANSWER hydrogen fusion never begins in their core 46. The most common type of stars in our galaxy are: - ANSWER low-mass stars 47. What methods are used to transport energy from the core of the Sun to its surface? - ANSWER radiation and convection 48. The dark matter in galaxies is much more ___________________ than the luminous material. - ANSWER extended in radius 49. AGNs appear to be powered by: - ANSWER supermassive black holes 50. H-R diagram is a graph of _____________ for stars. - ANSWER luminosity vs. temperature 51. On an H-R diagram, where are the stars with the smallest radii located? - ANSWER in the lower left corner 52. Hydrostatic equilibrium is a balance between: - ANSWER pressure and gravity 53. Which layer of the sun makes up the majority of its interior? - ANSWER the radiative zone 54. Sunspots appear dark because they have _________ than the surrounding gas. - ANSWER lower temperatures 55. The Maunder Minimum was a 60-year period when: - ANSWER almost no sunspots occurred on the Sun 56. The temperature of the __________ is much hotter than any other layer in the solar atmosphere. - ANSWER corona 57. Density, temperature, and pressure increase as you move inward in the interior of the Sun. This means that the force of gravity (Fg=GMm/r2), __________________ as you move inward toward the core. - ANSWER increases