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Astrophysics

Astrophysics. Introduction to the Universe. 1. Describe the shape of the orbits of the planets. Planetary orbits are elliptical, with the sun located at one of two foci Most elliptical - Mercury, Pluto Least elliptical - Earth.

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Astrophysics

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  1. Astrophysics Introduction to the Universe

  2. 1. Describe the shape of the orbits of the planets. • Planetary orbits are elliptical, with the sun located at one of two foci • Most elliptical - Mercury, Pluto • Least elliptical - Earth

  3. 2. Pluto’s orbit crosses the orbit of Neptune. Why don’t they have a high probability of colliding? • The planes of the orbits are different. • For example, Pluto’s orbit has a 17 degree inclination with the Earth’s orbit

  4. 3. Where is the asteroid belt? Describe the theories on its existence. • The asteroid belt is between the orbits of Mars and Jupiter • One theory - it was formed by the disruption of one planet into many pieces • Another theory - effect of Jupiter - Jupiter’s large mass prevented the material from forming into a planet

  5. 4. List the planets in order of increasing distance from the sun, and in order of decreasing radius. • Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, Pluto • Jupiter, Saturn, Uranus, Neptune, Earth, Venus, Mars, Mercury, Pluto

  6. 5. What is an astronomical unit? • One astronomical unit (AU)is the distance between the sun and the earth • 1 AU = 1.50 x 1011 m

  7. 6. What is the order of magnitude of the ratio of the mass of Jupiter to the mass of Pluto? • Mass of Jupiter 1.90 x 1027 kg • Mass of Pluto 1.5 x 1022 kg

  8. 7. Which planet is closest in size (radius) to the earth? • Radius of the earth 6.38 x 106 m • Radius of Venus 6.05 x 106 m

  9. 8. Which planet has the least acceleration due to gravity? Why? • Pluto - it has the smallest mass

  10. 9. Approximately how many times more massive is the earth than Mars? • 1.000/0.108 ~ 10

  11. What is a light year (ly)? What is a parsec (pc)? • Light year (ly) - the distance travelled by light in one year. • 1 ly = (3 x 108 m/s) x 3600 s/hr x 24 hr/day x 365 days/yr = 9.46 x 1015 m • Parsec (pc) - distance at which 1 AU subtends an angle of 1 arcsecond (1 arcsecond = 1/3600 of a degree) • 1 pc = 3.26 ly = 3.09 x 1016 m

  12. 11. How is a stellar cluster different from a constellation? • Stellar cluster - group of stars physically near each other in space, created by the collapse of the same gas cloud • Constellation-group of stars in a recognizable pattern that APPEAR to be near each other

  13. 12. Distinguish between a black dwarf and a white dwarf. • Black dwarf - the remnant of a white dwarf after it has cooled down - low luminosity • White dwarf - red giant at the end of its evolution -small, dense, no nuclear reaction, very hot but low luminosity

  14. 13. What is a main sequence star, and how is it different from a red giant? • Main sequence star - normal star undergoing nuclear fusion of hydrogen to helium • Red Giant - a main sequence star becomes a red giant- large,reddish star, nuclear reactions involve fusion of helium into heavier elements

  15. 14. Why does the sun always rise in the east and set in the west? • The earth rotates from west to east

  16. 15. What is the celestial sphere? Why doesn’t Polaris appear to move? • Celestial sphere - a hugh sphere surrounding and rotating around the earth on whose surface the stars and constellations are embedded. • Polaris is on the celestial North Pole so it appears not to move.

  17. 16. Why do the constellations in the sky change during a year? • The earth revolves around the sun, so the earth’s night hemisphere points at different constellations

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