What is an orbit?

An orbit is not magic and it is not "zero gravity". It is falling — but moving sideways so fast that you keep missing the ground. Isaac Newton pictured a cannon on a very tall mountain: fire the ball gently and it lands nearby; fire it faster and it lands farther; fire it fast enough and the ground curves away beneath it just as quickly as it falls. Now it never lands. That is an orbit.

Two ingredients make every orbit: a central mass pulling inward (gravity) and a sideways velocity carrying you around. Take away the sideways motion and you plummet straight down. Take away gravity and you fly off in a straight line. An orbit is the balance between the two.