4 Kepler’s Laws Why you can get there from here.

4 Goals Kepler: Astrologer turned Astronomer. Kepler’s Laws. Proof of Kepler’s Laws.

4 Astrology to Astronomy Kepler was an astrologer. Looked for Perfect Solids Wants did not match with Observations (tests). Followed the facts where they led. The result works.

4 Kepler’s Laws 1.Orbits are always ellipses. 2.Sweep out equal areas in equal times. 3.The period of orbit is related to average separation.

4 Concept Test Kepler’s second law says “a line joining a planet and the Sun sweeps out equal areas in equal amounts of time.” Which of the following statements means nearly the same thing? a.Planets move fastest when they are moving toward the Sun. b.Planets move equal distances throughout their orbit of the Sun. c.Planets move slowest when they are moving away from the Sun. d.Planets move farther in a given time when they are closer to the Sun. e.Planets move the same speed at all points during their orbit of the Sun.

4 Gravity is the Force Newton’s Law of Gravity: So: Becomes:

4 Concept Test You want to launch a satellite into geostationary orbit (i.e., it always stays over the same spot on Earth as the Earth turns), what is the only thing you need to know in order to determine how far from the Earth the satellite needs to orbit? a.The mass of the satellite. b.The period of the satellite’s orbit. c.The mass of the Earth. d.The mass of the Sun. e.The average distance to the Sun.

4 Concept Test You discover a new comet around our Sun: –Average distance from Sun = 4 AU. –What is the period? a.1 year b.4 years c.8 years d.64 years e.Don’t have all the necessary information.

4 Concept Test In a few billion years the sun will expand. In order to avoid the destruction of the Earth, humanity moves the Earth 5 times farther away from the Sun than it is now. How long will it take the Earth to go around the Sun at this new distance? a.1 year b.5 years c.11 years d.15 years e.125 years

4 Orbital Mechanics Courtesy David Crisp and WFPC2 Science Team

4 Courtesy NASA/JPL/Cornell Mars

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4 It Works Courtesy NASA/JPL/Cornell

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4 Spirit: View of Columbia Hills from floor of Gusev Crater

4 Spirit: In the Columbia Hills.

4 Opportunity: Eagle Crater in Meridiani Planum

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4 Opportunity: View of Endurance Crater

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4 Opportunity: View of sand Dunes in floor of Endurance Crater

4 Class Structure Investigate 4 Key Topics this semester: 1.Extrasolar Planets 2.Black Holes 3.The Big Bang 4.SETI

4 Class Structure During each topic: –Pieces in a puzzle. –Many pieces in several topics At the end of each topic: –See how pieces fit. –See how the scientific method is applied –What is the evidence –Have a test.

4 Homework #4 For Friday 20-Jan: Read Ty7, Ty8, B6.1 – 6.3 Do B6: Problems 2, 7, 15 Imagine the Sun’s surface suddenly became much hotter (while the Sun’s size remains the same). Compared to the light it now emits, the Sun would emit: a.More ultraviolet light but less visible light. b.More infrared light but less visible light. c.More visible light but less infrared light. d.Less infrared light and less ultraviolet light. e.More ultraviolet light and more visible light.