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DO NOW. What is an astronomical unit? How big is an astronomical unit? How was the universe created?. How do we measure the motion of the earth?. Rotation Revolution Precession. Rotation. Turning or spinning of a body (object in space) on its axis RESULTS Day & Night 24 hours.

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  1. DO NOW What is an astronomical unit? How big is an astronomical unit? How was the universe created?

  2. How do we measure the motion of the earth? • Rotation • Revolution • Precession

  3. Rotation • Turning or spinning of a body (object in space) on its axis RESULTS • Day & Night • 24 hours

  4. Revolution • Motion of a body, such as a planet or moon, along a path around some point in space. RESULT • Earth revolves around the sun at 107,000 km/hr • Average distance 150 million Km (1 AU)

  5. Revolution Ellipse – Earth’s distance varies Earth closest to sun ~ Jan 3 (147 mill. Km) Earth furthest from sun ~ July 4 (152 mill. Km)

  6. Precession • Earth’s Tilt = 23.5degrees • Wobbles like a top • Slight movement (over 26,000 years) between 22 – 25 degrees

  7. What causes earth’s seasons?* • Tilt of the earth • Hemisphere pointed toward sun = summer

  8. How do bodies move in space?

  9. Kepler’s Laws • Path of each planet around the sun = ellipse *Sun at one of the foci

  10. Kepler’s Laws 2. Planet speeds up as it is closer to the sun, slows down further away

  11. Kepler’s Laws

  12. Kepler’s Laws 3. The length of time it takes a planet to orbit the sun (orbital period) & its distance to the sun are proportional

  13. Kepler’s Laws T2 = AU3

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