The Solar System, stars and the Pole Star

At the centre of the Solar System is the Sun – the nearest star to Earth – and eight planets orbit it. The Sun is a ball of very hot gas made mostly of hydrogen and helium and is Earth’s main source of light and heat. The Sun–Earth distance is about 150 million km; light covers it in about 8 minutes 20 seconds. Earth moves round the Sun at an average 29.8 km/s, anticlockwise, along an elliptical orbit. The planets in order from the Sun: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune. The first four are the small (terrestrial) planets: relatively small, with solid surfaces and few or no moons. The next four are the giant planets: huge, with many moons. Between Mars and Jupiter lies the asteroid belt: asteroids are irregular rock-and-metal bodies. A comet has a head (a nucleus of ice and dust) and a tail; it gives off no light of its own but reflects sunlight. Pythagoras, Eratosthenes, Hipparchus, Beruni, al-Khwarizmi, al-Farghani, Ulugh Beg, Copernicus, Galileo, Kepler and others studied the heavens.