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.

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.

How many times does the earth rotate about its axis in a year? 365.242 + 1 = 366.242 Sun Earth

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

What causes the seasons? Earth Sun

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

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.

Angle of Sunlight

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

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.

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