Earth's Revolution

In addition to rotating on its axis, the Earth also travels around the sun in a path called an orbit. The motion around the sun along its orbit is called a revolution. The amount of time it takes for a single trip around the sun is called a period of revolution. The period for the Earth to revolve around the sun is 365.24 days or one year. The .24 days is why every four years February has 29 days.

Earth's tilted axis causes the seasons. Throughout the year, different parts of Earth receive the Sun's most direct rays. So, when the North Pole tilts toward the Sun, it's summer in the Northern Hemisphere. And when the South Pole tilts toward the Sun, it's winter in the Northern Hemisphere.

Earth's Rotation

Each planet rotates, or spins, on an imaginary line called its axis. Earth's axis is tilted at an angle of 23.5 degrees.

The rotation of the Earth on its axis causes day and night. As the Earth rotates, only one-half of the Earth faces the sun at any given time. The half facing the sun is light (day) and the half facing away from the sun is dark (night). Because the earth rotates from west to east, we see the sun rising every day in the east and setting in the west. It takes the earth 24 hours to make one complete rotation. That is why 24 hours make a day.