1. Rotation (Ro ‘Day’ tion)
An axis is the imaginary line that passes through the center of a planet from pole to pole.
The spinning of a planet on its axis is called rotation.

2. Earth’s rotation
The Earth rotates on its axis every 23 hours & 56 minutes.
One day on Earth is one rotation of the Earth.
Day on Earth is when our side of the Earth faces the sun.
Night on Earth is when the side of Earth we are on faces away from the sun.

3. How many times does the earth rotate about its axis in a year?=
Sun
Earth

4. As seen from the North Pole, which direction does the earth rotate?
Counter-clockwise
Sun
Earth

5. What causes the seasons?
Earth
Sun

6. Changes in sunlight
While the North Pole is pointed away from the Sun, Earth’s axial tilt causes the Southern hemisphere to experience summer.

7. Angle and light
Each surface gets the same amount of light, but in the top image, the light is spread out over a larger area.
In the bottom image, the light is concentrated on a smaller area.

8. Angle of Sunlight

9. How do we know the earth is rotating?
Foucault Pendulum (1851)
Coriolis Effect
Wind Patterns
Projectile Deflection

10. Revolution (Revolu ‘Sun’)
All of the planets orbit, or revolve, around the Sun in the same direction (counter-clockwise).
A year is the time it takes a planet to complete one revolution around the Sun.

13. How do we know the earth orbits the sun?
Annual Parallax of the Stars (1837) - nearby stars appear to move
Aberration of Starlight (1727) - change in apparent direction of stars, cf: raindrops