1. Ideas About Our Solar System:
Past and Present

2. GREEK ASTRONOMERS: Aristotle & Ptolemy
GEOCENTRIC SYSTEM:
GEO = Earth
CENTRIC = Center
Earth was at the center of the solar system
Earth was stationary (doesn’t move)
The sun, moon, and other planets revolved around Earth.
CELESTIAL SPHERE:
Universe is shaped like a closed ball with Earth at the very center.
Stars were attached to the inside walls of the sphere.
An astronomer is someone who studies outer space.

3. Early astronomers were able to see 5 planets from Earth with the naked eye!
Mercury
Venus
Mars
Jupiter
Saturn
There were NO telescopes until the 17th Century (1600’s)!!

4. NEW IDEAS ABOUT OUR UNIVERSE
COPERNICUS:
Believed that we had a Heliocentric Universe
~The Sun was at the center of our solar system
~ Planets move around the sun
GALILEO:
First astronomer to use a telescope!
Agreed with Copernicus’ heliocentric theory
Helio = Sun Centric = Center Heliocentric = Sun at the Center

5. 1600-Johannes Kepler discovered the shape of planetary orbits!
Planets DO NOT move in a circular orbit (path) around the sun.
Planets DO move in an ELLIPTICAL (oval-shaped) orbit around the sun.
ellipse

6. What keeps the planets moving around the sun?
GRAVITY:
The force that attracts all objects toward each other
*Larger objects pull harder on smaller ones.
First discovered by Isaac Newton
INERTIA:
The tendency of a moving object to move in a straight line or a stationary object to remain in place
*First discovered
by Galileo
inertia
gravity
*Isaac Newton stated that the planets stay in orbit around the sun because the sun’s gravity pulls on them while their inertia keeps them moving forward.
VIDEO

7. REVOLUTION & ROTATION What’s the Difference?
*Revolve = orbit (path) Rotate = spin
Planets ROTATE
on an invisible AXIS.
Planets REVOLVE around the sun in a counter clock-wise direction.
Moons REVOLVE around planets.
axis
moon
*Most planets, like Earth, rotate COUNTER-CLOCKWISE
earth

8. BECAUSE OF THESE INVENTIONS…
Telescopes
Satellites
Space Probes
Rockets
Space Shuttle
We have been able to do these things:
Discovered that there are 3 more planets: Uranus,Neptune, and Pluto
Man has traveled to the MOON!
Sent probes (machines--NOT man) to learn about Mars.
Study the sun, comets, asteroids, and other mysteries of outer space.

9. QUIZ!!! 1) What is an astronomer?
2) Who were the Greek astronomers that believed that the sun, moon and all the planets revolved around the Earth?
3) What was their theory called?
4) Which two early astronomers believed that the sun was at the center of the solar system?
5) What was their theory called?
6) What is the shape of planetary orbits?

10. QUIZ!!! 7) Draw the Earth REVOLVING around the sun.
8) Another word for rotate could be _______.
9) Which force keeps planets moving in a STRAIGHT LINE?
10) Which force PULLS planets toward the sun?
11) Name two things we have been able to do because of telescopes, satellites, space probes, rockets, and the space shuttle.
12) GEO= ________ HELIO= _________