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Review for Midterm I. Please press “1” to test your transmitter. 1 2 3 4 5. :10. 0 of 250. Within 100 AU from the sun, we find …. Only the terrestrial planets The terrestrial planets and the asteroids All (terrestrial and Jovian) planets

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  1. Review for Midterm I Please press “1” to test your transmitter. • 1 • 2 • 3 • 4 • 5 :10 0 of 250

  2. Within 100 AU from the sun, we find … • Only the terrestrial planets • The terrestrial planets and the asteroids • All (terrestrial and Jovian) planets • The entire solar system, including the Oort Cloud • The entire solar system, plus several neighboring stars. :10 0 of 250

  3. 0 The Solar System Approx. 100 AU

  4. Which of the following is the largest system? • A supercluster • The solar system • Jupiter • The Milky Way • The Local Group :10 0 of 250

  5. 0 The Universe on Very Large Scales Clusters of galaxies are grouped intosuperclusters. Superclusters formfilamentsand wallsaround voids.

  6. 8.45*106 equals • 845,000,000 • 84,500,000 • 8,450,000 • 845,000 • 1 AU :10 0 of 250

  7. Mercury, Venus, Earth and Mars are collectively called the … • Marsian Planets • Terrestrial Planets • Near-Sun Planets • Outer Planets • Minor Planets :10 0 of 250

  8. 0 Two Kinds of Planets Planets of our solar system can be divided into two very different kinds: Terrestrial (earthlike) planets: Mercury, Venus, Earth, Mars Jovian (Jupiter-like) planets: Jupiter, Saturn, Uranus, Neptune

  9. What is unusual about Venus’ orbit or rotation? • It rotates clockwise, opposite to all other planets. • It rotates counterclockwise. • It orbits around the sun clockwise. • It is inclined against the ecliptic by 10o. • 1. and 3. :10 0 of 250

  10. 0 Planetary Orbits and Rotation Retrograde rotation Tipped over by more than 900 Mercury and Pluto: Unusually highly inclined orbits

  11. From Houston, TX (latitude +30o), you see the celestial North pole • 30o above the southern horizon • 60o above the northern horizon • 30o above the northern horizon • 60o above the northern horizon • At the zenith. :10 0 of 250

  12. 0 Athens, OH: l ≈ 390 Celestial North Pole Celestial Equator 510 390 Horizon Horizon North South

  13. How is the wobbling (26,000 year) motion of the Earth’s axis called? • Terrestrial Tumbling • Epicycle • Procession • Topping • Precession :10 0 of 250

  14. 0 Precession Gravity is pulling on a slanted top. => Wobbling around the vertical. The Sun’s gravity is doing the same to the Earth. The resulting “wobbling” of the Earth’s axis of rotation around the vertical to the Ecliptic takes about 26,000 years and is called precession.

  15. The sidereal orbital period of the moon is the time it takes for the moon to … • Orbit once around the sun. • Rotate once around its axis, relative to the Earth. • Orbit once around the Earth, back to the same lunar phase. • Orbit once around the Earth, back to the same position with respect to the distant (fixed) stars. • Orbit once around the center of the Milky Way. :10 0 of 250

  16. 0 The Phases of the Moon 27.32 days • The Moon orbits Earth in a sidereal period of 27.32 days. Moon Earth Fixed direction in space

  17. 0 The Phases of the Moon Fixed direction in space 29.53 days Earth Moon Earth orbits around Sun => Direction toward Sun changes! • The moon’s synodic period (to reach the same position relative to the sun) is 29.53 days (~ 1 month).

  18. Spring tides occur at the time of … • Spring. • Noon and Midnight. • Full and New Moon. • First and last quarter moon. • 2. and 3. :10 0 of 250

  19. 0 Spring and Neap Tides • The Sunis also producing tidal effects, about half as strong as the Moon. • NearFull and New Moon, those two effects add up to causespring tides • Near first and third quarter, the two effects work at a right angle w.r.t. each other, causingneap tides. Spring tides Neap tides

  20. An annular solar eclipse happens when … • The Earth is at perihelion and the moon is at perigee. • The Earth is at aphelion and the moon is at perigee. • The Earth is at perihelion and the moon is at apogee. • The Earth is at aphelion and the moon is at apogee. • Every solar eclipse is annular. :10 0 of 250

  21. 0 Earth’s and Moon’s orbits are slightly elliptical: Apogee = position furthest away from Earth Earth Perihelion = position closest to the sun Moon Perigee = position closest to Earth Sun Aphelion = position furthest away from the sun (Eccentricities greatly exaggerated!)

  22. 0 Annular Solar Eclipses The angular sizes of the Moon and the Sun vary, depending on their distance from Earth. Perigee Apogee Aphelion Perihelion When the Earth is near perihelion, and the Moon is near apogee, we see an annular solar eclipse.

  23. Ptolemy’s model of the “Universe” … • Was heliocentric. • Was geocentric. • Contained epicycles. • Described the planetary orbits as ellipses. • 2. and 3. • 1. and 4. :10 0 of 250

  24. Ptolemy:Geocentric model, including epicycles 0 Central guiding principles: 1. Imperfect, changeable Earth, 2. Perfect Heavens (described by spheres)

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