What shape is the Earth’s orbit?

• The Earth’s orbit around the sun is shaped like an ellipse.

• A circle (for the most part).

• Ex: If the orbit is a circle, what causes the seasons?

How does sunlight strike the Earth’s surface?

• Near the equator, sunlight strikes Earth’s surface more directly and is less spread out than near the poles.

• Please draw this picture in your notes.

What causes the seasons?• Earth has seasons because Earth is tilted as it

revolves around the sun – not because it is closer to or farther from the sun! How much is it tilted?

What is equinox and solstice?

• Equinox = neither end of Earth’s axis is tilted toward the sun.

• Solstice = North or south end is tilted toward the sun.

• Gravity is a force that attracts all objects toward each other.

What is gravity?

• The strength of the force of gravity between two objects depends on two factors: the masses of the objects and the distance between them.

What determines the strength of gravity?

What is the law of gravitation?

• Every object in the universe attracts every other object.

• Newton concluded that two factors–gravity and inertia–combine to keep the moon in orbit around Earth.

• Dance, Dance (Gravity and Inertia)

If gravity is constantly pulling, what keeps the moon in orbit?

What is inertia?• The tendency

of an object to resist a change in motion.