Have you ever played with a ball on a string? If you have, then you know that as it spins, the ball pulls against the string.

As long as the ball is moving it continues to spin round in the air. The planets are heavenly bodies. A planet moves like the ball as it turns around the sun. But where is the string? Three isn't one.

There is an invisible force which pulls the planets towards the sun. This is called the terrestrial force of attraction. The sun pulls the planets; they pull against this force like the ball on the string. A Polish scientist, Copernicus, was the first to discover that the orbits of the planets formed a circle around the sun. Galileo agreed and proved these beliefs. In 1609, Kepler noticed that the or bits of the planets were not circular but elliptical. Then an Englishman Isaac Newton, explained how the system kept its shape.

Every particle of matter pulls on the others: that is the law of gravity around the sun.
Each planet in our Solar System turns in its orbit around the sun. This orbit is in the shape of an ellipse. A planet has no light of its own. The sun is light, heat and life.