Science
Why does Earth orbit the Sun?
Earth keeps moving through space while the Sun’s gravity pulls it inward. That combination bends Earth’s path into an orbit instead of a straight line.
Two things happening at once
Imagine an arrow showing Earth’s motion along its path, and another pointing toward the Sun. The first shows where Earth is moving at that moment. The second shows the direction of the Sun’s gravitational pull. Gravity continually changes the direction of Earth’s motion.
Earth is not sitting still above the Sun. Its sideways motion matters: it keeps moving as gravity bends its path. An orbit is sometimes described as continuous falling around another object.
A drawing is a model
This drawing uses a circular path with the Sun in the middle to show the idea clearly. Real planetary orbits are ellipses, and the Sun lies at a focus of the ellipse. Earth’s orbit is close to circular. Sizes, distances and motion here are simplified.
Have a go
Try explaining your answer before opening the hint.
If the Sun’s pull suddenly vanished in this simplified model, which way would Earth move?
Along a straight line tangent to its path at that moment, rather than continuing around the circle. This thought experiment ignores other gravitational influences.
Does gravity stop when Earth is in orbit?
No. Gravity keeps acting and changing the direction of Earth’s motion.
Why do we draw both an inward arrow and a forward arrow?
They represent different things: the inward arrow is the gravitational pull; the forward arrow shows motion along the path.
Draw and explain
Draw a Sun and an Earth with space between them. Add an arrow toward the Sun and an arrow along Earth’s path. Explain what each arrow represents to someone else.
Read more: NASA Space Place: What is gravity? and NASA: Facts about Earth.