Kepler’s three laws Kepler’s three laws explain how planets orbit around the sun. These laws are common to any body orbiting around a massive body

First law: the law of orbit ALL PLANETS MOVE IN ELLIPTICAL ORBITS WITH THE SUN AT ONE FOCUS An orbiting body travels in an elliptical path around a central massive body which is located at one of the ellipse’s foci

SECOND LAW: the law of areas The line joining the planet and the sun sweeps out equal areas during equal intervals of time This means that the closer the planet is to the sun the faster it runs

THIRD LAW (the law of periods)

What’s the cause of planets motion? Kepler’s laws are very important, but they only describe a situation, they don’t give any explanation of the causes of planets’ motion. Isaac Newton gave the answer: the force that keeps the Earth close to the Sun is the same force that makes apples fall from the trees onto the ground: THE UNIVERSAL GRAVITATIONAL FORCE