Solar System

            The solar system consists of the sun and all the planets and other bodies that revolve around it. It is shaped like a disk with the sun at its center.

            The largest objects orbiting the sun are the nine planets, Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto. Some planets have moons – natural bodies that revolve around them. Other bodies orbiting the sun include thousands of tiny objects called asteroids and comets – chunks of ice, rock, and dust. The solar system also contains dust and gases left over from when it was formed.

            All the planets and most asteroids revolve around the sun in nearly circular orbits (paths) that are in nearly the same plane. They all move in counterclockwise orbits, as seen from “above.” Some moons have clockwise motion.

Theories about the solar system

            Five planets – Mercury, Venus, Mars, Jupiter, and Saturn – are regularly visible from Earth and have been known since ancient times. Around 300 B.C. some ancient Greek scientists suggested that the sun was the center of the solar system. Until the mid-1500s, however, most people believed that the Earth was the center of the solar system, and that everything else revolved around it. Then, in 1543 the Polish astronomer Nicolaus Copernicus (1473-1543) figured out that the Earth and the other planets traveled around the sun in circular orbits.

            By 1618 further discoveries by the German astronomer Johannes Kepler (1571-1630) led to what became known as Kepler’s three laws of planetary motion. The English scientist Isaac Newton (1642-1727) used a form of math called calculus to show that gravity, the force that holds objects to the Earth, also holds the planets in their orbits round the sun.

            The German astronomer Johannes Bode (1747-1826) discovered a mathematical relationship in the distances of the planets from the sun. In 1781, when the English astronomer William Herschel (1738-1822) discovered Uranus, it fit into Bode’s pattern, as did many asteroids when they were discovered. Astronomers discovered Neptune in 1846 and Pluto in 1930.