Throughout history, philosopher, scientists, engineers and imaginative writers have speculated about the nature of our unfolding Universe.The first astronomical records kept with surprising accuracy 4000 years ago in Mesopotamia, were used more for astrology than science. Wars were planned according to the position of Saturn or Mars, and the ability to offer such advice gave astrologers great power. Claudius Ptolemy, who worked in Alexandria in the second century AD, put forward theories that lasted some 1400 years. He assumed that the Earth was spherical, that it was the centre of the cosmos, and that a natural motion – rotation – drove all planets. He was the first to design a system, named after him, that accurately predicted planetary motions.

When Nicolaus Copernicus proposed that the Sun controlled the planetary system, he was accused of heresy. A luckless follower, Giordano Bruno, was burned at the stake. The courageous and inspiring work of Copernicus was followed by that of Tycho Brahe, a Danish nobleman.

Brahe and his assistants recorded precise planetary positions for more than twenty years. His work led him to doubt the Copernican model of the cosmos, and he drew up a new one in which the Sun moves round the Earth but all other planets orbit the Sun.

Brahe trained Johannes Kepler, who produced his famous and quite radical laws of planetary motion . In 1 609 , Kepler published his Astronomia Nova (New Astronomy) which overturned the belief that the solar system moves uniformly and in perfect circles. Astronomy became a science based on physics.

Italian mathematician Galileo Galilei, the first to use the telescope in astronomy, built an instrument that made distant objects look thirty times closer. He saw the Moon, planets and stars as no one had seen them before. Galileo advanced theories of terrestrial motion – acceleration, velocity, speed and inertia – and opened the door for Newton and other renowned explorers of space.

Born on Christmas Day 1642 , Isaac Newton, a great mathematician and thinker, ended the idea that the Earth and other planetary bodies are separate and independent. He is best known for i- discovering the law of gravity, but also he solved the problems of planetary motion. A close friend, Edmond Halley, used Newton’s laws to work out the orbit of the comet that bears his name.