The Universe Essay Research Paper Student — страница 3

  • Просмотров 282
  • Скачиваний 5
  • Размер файла 18

is believed to be in the range of 50 to 100 km/s/106 pc. 19. With respect to a black hole, what is a singularity? Your Answer: The center of a black hole. A singularity is the center of a black hole. It is a single point to which a very massive star has been reduced by a process called gravitational collapse. Its properties include a very large concentrated mass, an infinite density, and a radius that is actually associated with its event horizon, not the singularity itself. 20. What is an event horizon? Your Answer: The boundary surrounding a black hole. An event horizon is the boundary surrounding a black hole. Once inside the event horizon, no physical matter or radiation, not even light, can ever escape, hence the name black hole. 21. The lifetime of a star on the main

sequence a. is infinite. b. is inversely proportional to the star’s total mass. c. cannot be determined. d. depends on where it is located within a galaxy. Correct 22. The rotational period of the equatorial region of the Sun is about 25 Earth days. Astronomers on Earth have determined this by a. observing the east-to-west motion of sunspots. Correct b. using the Doppler shift of spectral lines emitted from the center of the Sun’s photosphere. c. measuring the motion of the solar wind. d. observing differences in the Sun’s surface temperature. 23. A Hertzsprung-Russell diagram, or H-R diagram, shows the relationship between the a. absolute magnitude of a star and its velocity. b. velocity of a star and its distance from Earth. c. relative size of a star and its rotational

speed. d. luminosity of a star and its temperature. Correct 24. Hubble classified the galaxies into three general types. These types are a. ellipticals, whirlpools, and sphericals. b. sphericals, spirals, regulars. c. ellipticals, spirals, irregulars. Correct d. near, moderate, far. 25. A black hole is best described as a. an empty volume of space. b. an invisible hole in the universe. c. a singularity surrounded by an event horizon. Correct d. the central core of a quasar that is invisible. 26. Describe two surface features of the Sun that can be seen from Earth through a properly shielded telescope. Your Answer: Sunspots dark spots on the sun which are strong magnetic fields. Prominences great eruptions at the edge of the sun s surface. The two most distinct features of the

Sun’s surface that can be seen through a properly shielded telescope are: sunspots – dark regions on the Sun’s surface characteristic of strong magnetic activity and showing cooler temperatures than the surrounding areas. prominences – great eruptions at the edge of the Sun that are connected with violent storms in the chromosphere. 27. What process produces the energy necessary to make our Sun shine? Explain briefly how this process works. Your Answer: The Sun shines because of the fusion reactions that take place in its core. The Sun shines, that it emits radiant energy into space, because of heat produced in fusion reactions taking place deep in the core of the Sun. This fusion process converts hydrogen into helium by taking four protons (hydrogen nuclei), and

combining them into a helium-4 nucleus in a process called the proton-proton chain. 28. Describe the celestial sphere, and tell how it is oriented with respect to Earth. Your Answer: Imaginary transparent that surrounds the Earth which planets can be positioned. A celestial sphere is a huge, imaginary, transparent globe that surrounds Earth upon which all of the fixed stars are placed and upon which the positions of the Sun, Moon, and planets can also be assigned. If this imaginary sphere is allowed to rotate, it can be used to simulate the motion of the stars and planets as they appear to move around Earth each day. It must be remembered that it is really the Earth’s rotational motion on its own axis that causes this apparent motion. The celestial equator lies directly above

Earth’s equator and the north celestial pole and south celestial pole are positioned directly above Earth’s North and South poles, respectively. 29. What are constellations, and how have they acquired their names? Your Answer: Patterns of stars that are named after the shapes they represent. There are 88 constellations that are composed of certain patterns of stars as pictured from Earth. These patterns cover well-defined areas of the sky, and any one star can only be part of one of these established groups. The constellations are named after figures or creatures as seen in the sky by the early Babylonians and Greeks and sometimes carry the names of ancient gods and mythical animals. 30. Where does the red giant phase come in the overall life cycle of a star? Your Answer: