|In 2009, it is 400 years since Galileo Galilei (1564-1642) pointed a telescope at the sky and saw that the Earth was only one of many planets and not the centre of the universe.
His observation was the start of a revolution which changed Man's perception of the world for ever. The United Nations has proclaimed 2009 the International Year of Astronomy and astronomy is also the theme of this year's Europa stamps. The word astronomy comes from Greek and means the science of celestial bodies. However astronomy is more than that. It also combines other sciences and uses them to study everything that is to be found outside our own planet. Astronomy is thus the most comprehensive of all sciences.
The Greek philosopher Aristoteles (384-322 BC) believed that the Earth was the centre of the universe and that all the celestial bodies circled round it. Aristoteles was highly respected and his ideas were quickly accepted. Many hundreds of years were to pass before anyone was able to challenge Aristoteles' geocentric theory. Towards the end of the Middle Ages more and more importance was being attached to accurate scientific observation in astronomy. Nicolaus Copernicus (1473-1543) was the first to understand the true order of the planets in the solar system. The Earth was not the centre of the universe but the third planet from the Sun.
Galileo Galilei's observations in 1609 were the final breakthrough for the theory that the Sun is the centre of the universe. Although his book, Dialogue concerning the Two Chief World Systems, describes how the planets orbit round the Sun, it was still not known why they do so. Enter Isaac Newton (1642-1727), who developed laws of motion and gravitation and established that gravity depends on the object's mass. An object with a greater mass will attract a smaller object. The planets are therefore held in orbit round the Sun by the Sun's gravitation. Newton's ideas were ground-breaking, but his theories about gravity did not explain everything. More details fell into place when Albert Einstein (1879-1955) established his theory of relativity in 1905.
More recently, the space race between the Soviet Union and the USA marked the start of some amazing space exploration. Astronomers will claim that the zenith (so far) was reached in 1990 with the launching of the giant Hubble space telescope. After its initial problems ('nearsightedness'), the telescope has been an enormous success. Photos have been taken of stars being born, of black holes and of supernovas (stellar explosions). The minute these fantastic photos have been taken, NASA makes them available to us all on the Internet.