1. Arrangement & Movement of Objects in Our Solar System …and who figured it all out?

2. Rotating vs. Revolving Planets ROTATE (spin like a top) on an imaginary AXIS Planets REVOLVE around the SUN. This means they travel around the sun in a path, like they are running around on a track. Planets revolve around suns. Moons revolve around planets. ALL of them rotate while they revolve. One complete rotation takes 24 hours One complete revolution takes 365 ¼ days!

3. WHAT IS AN ORBIT? AN ORBIT is the PATH each planet follows to REVOLVE around the sun. Every planet has ITS OWN ORBIT. Orbits are NOT circular-shaped. The shape of each planet’s orbit is called an ELLIPSE. An ellipse is an OVAL SHAPE. The closer a planet is to the sun, the shorter its orbit will be around the sun. Mercury takes 88 days to ORBIT the sun. Neptune takes almost 165 YEARS!

4. Which TWO FORCES keep planets in their orbit? INERTIA: Planets are all moving out toward outer space in a straight line. GRAVITY: -a pulling force The more mass an object has, the more gravity (pull) it has. The sun has a LOT of gravity, which causes the planets trying to move past it to be pulled towards it. The planets also pull a little on the sun! INERTIA GRAVITY

5. PTOLEMY & ARISTOTLE -The GEOCENTRIC Model- Ancient Greeks like Ptolemy & Aristotle believed that EARTH was at the center with the sun and all the planets revolving around it! They believed we were inside a closed, solid sphere with the stars pasted on the inside! This is called the GEOCENTRIC model of our solar system.

6. COPERNICUS & GALILEO The HELIOCENTRIC Model Around 1600, an Italian astronomer named Galileo designed one of the first telescopes & used it to make observations that proved the sun was at the center of our planetary system. This model of our planetary system is called the HELIOCENTRIC model. Around 1500, a Polish astronomer named Copernicus claimed Earth was NOT at the center of the solar system. He stated that the SUN was at the center, with all the planets revolving around it. This was very controversial as the church preferred the belief that Earth was at the center.