What are the motions of the Earth? motion.pdf · Earth and the Moon in Space •The Earth and the moon are part of the sun’s planetary system. •Pulled by the sun’s gravity,

What are the motions of the Earth?

Earth and the Moon in Space

• The Earth and the moon are part of the sun’s planetary system.

• Pulled by the sun’s gravity, the Earth-moon system revolves or travels in a closed path around the sun which is called an orbit.

• It is inertia that keeps the Earth in motion around the sun.

Earth’s Revolution A revolution is the movement of a planet or other body orbiting another body.

This determines the length of a year.

One complete revolution of the Earth around the Sun takes 365 ¼ days.

The Length of the Day • Earth’s rotation results in

day and night. • Half of Earth is always facing

the sun. • A day is defined as the time

that it takes the Earth to rotate once on its axis.

Earth’s Rotation

Because of the Earth’s rotation, the Sun appears to rise in the East and set in the West.

The Sun’s motion is East to West.

Seasons

Stop….think….

Why do we have seasons?

Why is summer warmer than winter?

Have you heard of Harvard? What do you know about it?

Listen to some Harvard graduates explain the seasons. It is an old clip…but a good one!

Earth in Space

As Earth orbits the sun, it rotates or spins on its axis.

The axis is an imaginary line

that passes through Earth’s center and its North and South Poles. Earth’s axis is tilted about 23 ½ °.

Earth’s Rotation

The North Pole of Earth always points toward Polaris or the North Star.

It is the brightest and last star of the Little Dipper.

The tilt of the Earth is responsible for the seasonal differences we see and feel throughout the year.

The Four Seasons: The Effect of the Tilt

of Earth’s Rotation Axis

Solstices and Equinoxes

Spring Equinox ~ March 21 Summer Solstice ~ June 21

Fall Equinox ~ September 22 Winter Solstice ~ December 21

The dates of the equinoxes and solstices

are only approximate dates. The actual length of a year is about 365 ¼ days. We have to add an extra day to a year every four years to keep the seasons synchronized with the Earth’s revolution (leap year).

What is the difference between orbit, revolution, and rotation?

A planet rotates on its own axis and revolves around the sun in a path called

an orbit.