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Astronomy is the scientific study of objects in space such as planets,stas,comets and black holes,using equipment such as telescopes and space probes. Early civilizations watched the stars and planets to predict the coming of the seasons.But it was the Ancient Greeks who first studied them as a science.The word astronomy comes from two Greek words meaning 'star laws'. COPERNICUS TO EISTEIN Modern astronomy began with Nicolaus Copernicus,who realize that the sun,not the Earth,was at the centre of our solar system.His ideas were published in 1543,the year he died.When Galileo Galilei used his newly invented telescope in 1610,he helped prove those ideas.In 1667,Isaac Newton put forward his laws of gravity,which explained how objects move in space,and Albert Einstein published a new theory of gravity in 1915 which led to ideas such as black holes and Big Bang. SIGNALS TO THE PLANETS Today's astronomers can calculate Earth's distance from other planets in our solar system by bouncing radar signals off the planets' surfaces and timing how long they take to return to Earth.The distance to faraway stars can be worked out from their brightness and by using a method called parallaxi(see diagram far right).