Eight planets race around the Sun in endless circles, held by an invisible pull — yet they never crash in. Today you'll learn why, then you will predict how the planets move.
Before we start — the planets never crash into the Sun or fly off into space — what do you think keeps them on their paths?
Our Sun sits at the centre, and eight planets travel around it along paths called orbits. The small rocky planets orbit close in; the giant gas planets orbit far out. (Earth is the third planet from the Sun.)
The Sun's gravity pulls every planet toward it — like an invisible string holding it in. Gravity is stronger when you're closer, so the close-in planets are pulled hard and whip around fast; the far-out planets are pulled gently and drift around slowly.
If gravity pulls planets inward, why don't they crash into the Sun? Because each planet is also racing sideways. Gravity bends that sideways motion into a curve — so the planet keeps falling around the Sun forever. That curved path is an orbit.