Earth's Orbit

 

	Picture Earth as it travels around the Sun—a rather small blue sphere with one moon. Earth is one of
	nine planets circling the Sun. The solar system is made of the Sun and its nine planets along with many moons, asteroids, and comets. The Sun, planets, and moons are all nearly spherical, or ball-shaped.
	The Earth and the other planets each follow a path called an orbit around the Sun. Orbits have elliptical paths. Elliptical describes a shape like a slightly flattened circle. Likewise, the Moon moves in an elliptical orbit around the Earth. Trace the elliptical shape of the orbit shown in the diagram in the margin above. Notice how the planet moves slightly closer to the Sun at certain parts of the orbit.
	One full orbit is called a revolution. Earth’s revolution around the Sun lasts for just a few hours longer than 365 days. This period may sound familiar to you. It is one year. Likewise, the Moon’s revolution around the Earth takes about 28 days. This is about a month. In fact, the wordmonth comes from the word moon.
	Just as gravity keeps you on the Earth, gravity keeps the Earth and other planets in their orbits around the Sun. Gravity also keeps the Moon orbiting around the Earth.