1. Geocentric/Heliocentric

2. Models to Explain Motion
Geocentric Model – Earth centered.
Planets, stars, and other objects revolve around Earth.
This model was able to explain the apparent motion of the stars, sun, and moon.
Could not explain retrograde motion and foucault pendulum motion.

3. Retrograde Motion
Retrograde motion is an apparent motion of planets (over weeks to months) when they appear to change position with respect to the background field of stars.

4. Retrograde Motion Cont…
Retrograde motion is caused by Earth and other planets revolution around the Sun in different orbits at different speeds.

5. Retrograde Motion of the Planets
Note: outer planets are slower

7. Models to Explain Motion
Heliocentric Model – Sun centered.
Earth rotates on an imaginary axis and revolves around the Sun.
The Moon revolves around Earth.
Explained all of the observations made by the scientists including retrograde motion.

9. Actual Earth Motion
Rotation – Earth spins on its axis from west to east at 15 degrees per hour.
The Sun, Moon, stars appears to move across the sky at a rate of 15 degrees per hour.
The Foucault pendulum and the Coriolis Effect confirm Earth’s rotation.

10. Foucault Pendulum A pendulum is a freely swinging weight.
Over a day, the direction of motion of a pendulum will appear to change. Actually, Earth is rotating under the pendulum.

12. Coriolis Effect
Coriolis Effect - the bending of winds and currents due to the rotation of Earth.
Northern Hemisphere, they bend to the right.
Southern Hemisphere, they bend to the left.

15. Evidence of revolution Different constellations throughout the year.
Earth’s Revolution
Earth revolves around the Sun once a year.
It revolves approx. 1° per day.
Earth is closest to the Sun on January 3rd. This is called the perihelion.
Earth is farthest to the Sun on July 3rd. This is called the aphelion.
Evidence of revolution
Seasons
Different constellations throughout the year.