Around and around the sun
The earth doesn’t just spin—it also moves through space.
Right this very moment, the earth is rushing through space at tremendous
speed—more than 66,000 miles (106,000 kilometers) an hour. It isn’t
going in a straight line, though. It’s whirling around and around the
sun, in a kind of stretched-out circle. This circle the earth makes
around the sun is called an orbit.
What makes the earth keep moving around and around the sun? Why doesn’t
it just fly off into space?
Everything in space pulls at everything else. This pull is called
gravitation. The bigger a thing is, the stronger its pull. The sun is
more than a million times bigger than the earth, so it tugs hard at the
earth. It is this strong tug that keeps the earth in orbit. If you
fasten some string to a ball, you can whirl the ball around and around,
to show the way the earth goes around the sun. The string is like the
pull of the sun’s gravity—it holds onto the ball. Even though the ball
is moving, it can only move in a circle.
The time it takes the earth to go all the way around the sun is a little
more than 365 days. This is what we call a year.
