Solar System Geocentric = Earth (geo) is center of universe Heliocentric = Sun (helio) is center of universe Which is correct? Heliocentric… proved by Copernicus and Galileo.

Solar Nebula Theory How to make a solar system: 1.Start with nebula = a large cloud of dust and gas. 2.The nebula begins to spin and contract from gravity. This creates a flattened disk. ie: pizza, skirt on spinning ice skater.

Solar Nebula Theory 3.The middle of the disk reaches high temp. and ignites! Nuclear Fusion = when lighter elements combine into heavier elements (Hydrogen + Hydrogen = Helium) 4. Voila… a star is formed.

Planet Formation Dust and rocks begin to clump together… like a snowball = accretion. Planetesimals = objects size of small moons with gravitational fields. Differentiation = dense materials sink to form core, light materials float and form crust.

Planets Definition (2006): 1.Must orbit around the Sun. 2.Enough mass to be a sphere. 3. Cleared the “neighborhood” around its orbit.

Planet Groups Terrestrial Mercury, Venus, Earth and Mars. -- Rocky surface -- Small diameter -- High density -- Few moons Jovian Jupiter, Saturn, Uranus and Neptune. -- No surface -- Large diameter -- Low density -- Many moons

Pluto Pluto resides in Kuiper Belt. In 2005, Eris (same size as Pluto) found in Kuiper Belt. Pluto does not clear out its orbit

Kuiper Belt Region located 30 to 55 AU (past Neptune). 1,300 objects discovered so far. May have over a trillion comets and 200 dwarf planets.

Elliptical Orbits All planet have elliptical (oval) orbits. Eccentricity = how flat 1.Two fixed points within ellipse (foci) 2.Sun is at one of the foci. Circle = 0 eccentricity Line = 1 eccentricity

Gravity Aristotle = heavy objects fall faster than light objects. Kepler = laws of planetary motion (didn’t know cause). Galileo = first to test “how objects fall” (didn’t know cause).

Isaac Newton Gravity is a force. From Galileo’s ideas he determines that the moon is falling into Earth, but keeps missing it (orbit). Thought experiment – gravity cannon.

Asteroids Rocky and Metallic objects that orbit the sun. Most located between Mars and Jupiter. Periodically destroy all life on Earth.

Comets Ball of dust and ice that revolves around the sun. “Dirty snowball”. Most come from Kuiper Belt and Oort Cloud… very far from Sun.

Exoplanet Exoplanet = planet orbiting another star. Over 1,075 confirmed so far. First rocky planet found.