2. Formation of the Solar System  Nebular Hypothesis – 12 billion years ago a giant nebula (cloud of gas & dust) rotated quickly, shrank, & compressed creating the sun and a planetary disc. As time passed, the disc condensed into small planets.  4.6 billion years ago, most planets had formed, including Earth!

3. Models for Our S.S.  Aristotle & Ptolemy 90-168 A.D. geocentric model of our S.S.  Earth is at the center  Copernicus 1473-1543 A.D. heliocentric model for our S.S.  Sun is at the center  Kepler Explained the motions of planets with 3 laws– observed planet orbits from different places on Earth

4. Kepler’s 1 st Law  Elliptical Orbits not Circular, with the Sun at one foci

5. Ellipse Geometry You do not have to copy this slide Minor Axis Major Axis Foci Eccentricity=How oval is it?

6. Kepler’s 2 nd Law  Perihelion- planet’s closest distance to Sun in orbit  Moves faster than @ aphelion  Aphelion- planet’s farthest distance from Sun  2 nd Law- “Equal Area Law” b/c the planet has to move faster closer to the sun to get an area equal to that of an area furthest from the sun Click below for an Animation! http://www.physicsclassroom.co m/mmedia/circmot/ksl.cfm

7. Kepler’s 2 nd Law: When a planet is closer to the Sun, it moves faster

8. Kepler’s 3 rd Law  The more distant a planet’s orbit is from the Sun, the slower it moves  Compares planets to one another  Period- time for one complete orbit around sun  Let’s see all three in action Let’s see all three in action

9. Measuring Distances in our S.S.  Astronomical Unit (AU) the distance from Earth to the Sun (150 million kilometers OR 93 million miles)  Things within our solar system are measure in A.U.’s

10. Other areas within our S.S. 1. The Kuiper Belt: [30-55 AUs] 1000s of objects s.a. dwarf planets and balls of ice/dust/gas (comets or “dirty snowballs”)- some get hurled towards the sun  comet’s tail always points AWAY from the sun b/c of the solar wind 2. Oort Cloud: [5,000-100,000 AUs] way past the Kuiper belt & Pluto; millions of comets that do not orbit the sun

11. S.S. FACTS 1. Inner planets- “terrestrial” planets 2. Outer planets- “gas giants” or “Jovian planets” 3. Saturn would float in a bowl of water (density is <1.0 g/cm³) 4. All outer planets have rings 5. Venus revolves around the sun quicker than it rotates on its axis (Its day is longer than its year!) 6. Venus is our “sister planet” b/c of its size and density 7. Venus is also known as the “morning star” b/c we can see it in the western sky in the morning

12. S.S. FACTS 8. Venus is the hottest planet b/c of a runaway Greenhouse Effect (too much gas!) 9. Uranus rotates on its side (spins like a bowling ball) 10. Neptune used to have a dark spot, like Jupiter, which was also thought to be a storm 11. Uranus & Neptune are about the same size 12. Jupiter is the largest planet

13. Size of planets in order from largest to smallest 1. Jupiter 2. Saturn 3. Uranus 4. Neptune 5. Earth 6. Venus 7. Mars 8. Mercury 9. Pluto (not a planet)

14. Why was pluto downgraded to a ‘dwarf planet’? 1. Too small ~1 mile across 2. Doesn’t fit the categories of “terrestrial” or “gas” planet- predominantly ice & resides in Kuiper belt (like a comet) 3. Not always the 9 th planet– its orbit is so eccentric that it crosses Neptune’s orbital path every 228 years & spends ~20 years being closer to the Sun than Neptune