The Solar System

Solar System Models•geocentric model: model of the solar system that states that the Earth is the center of the solar system–believed until 1600’s

•heliocentric model: model of the solar system that states that the sun is the center of the solar system and the planets revolve around it

•the stars don’t seem to move in our sky; planets do because they are much closer than stars

•planets move in an eastward movement

•sometimes planets appear to move in a backward movement, this is called retrograde motion

•a loop occurs because each planet travels around the sun at different speeds

Watch retrograde motion!

http://www.astro.uiuc.edu/projects/data/Retrograde/index.html

•The path a planet follows around the sun is called its orbit

Kepler’s Laws of Planetary Motion

•1st law : planets orbit the sun in a path called an ellipse

aphelion

perhelion

•astonomical unit: the average distance between the earth and the sun–150 million km

•2nd law: planets move fastest when they are closest to the sun in their orbits

•3rd law: the farther away a planet orbits, the longer the planet takes to revolve around the sun

•revolution: movement of the Earth around the sun–takes 365.24 days (1 year)

•rotation: spinning of Earth on its axis–takes 24 hours (1 day)–rotates counterclockwise

the Earth is tilted 23 ½ °on its axis. Either the Northern Hemisphere or Southern Hemisphere tilts towards the sun

•hemisphere that tilts towards the sun has summer (more direct sunlight

•hemisphere that tilts away from the sun has winter (less direct sunlight)

•summer solstice: longest sunlight hours of the year-June 21st-first day of summer

•winter solstice: shortest sunlight hours of the year- Dec. 21st- first day of winter

•spring equinox: equal amounts of day/night hours- March 21st- first day of spring

•fall equinox: equal amounts of day/night hours- Sept. 21st- first day of fall

•precession: slow circular motion of the Earth’s axis as it turns in space that traces a circle in space every 26 thousand years

• INNER PLANETS–also known as the terrestrial planets

–dense, small, have solid rocky surfaces, metal cores

•OUTER PLANET–also known as the Jovian Planets

– less dense, large, gaseous, thick atmosphere

“My Very Eager Mother Just Served Us Nine Pizzas”

To remember the order of the planets, just remember this sentence…

Other Objects in the Solar System

•comet: composed of dust, rock, frozen water, and gas

1. nucleus: glows by reflected sunlight

2.coma: hazy cloud that surrounds the nucleus

3. tail: gas and dust that always points away from the sun

Halley’s Comet

Hale-Bopp Comet

•asteroid: solid, rock-like mass, irregular in shape

•orbit the sun- most orbit between Mars and Jupiter in the asteroid belt

•Ceres is the largest asteroid

•meteoroid: rock or icy fragment moving through space–can be large as a boulder or as small as sand

•meteor: light made by meteoroid as it passes through Earth’s atmosphere

•meteorite: a meteoroid that lands on Earth– can be stone, iron, or stony-iron– most burn up before striking the

surface

iron meteorite

stone meteorite

stony-iron meteorite

•if they strike the Earth, they form impact craters (this is rare!)