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...work out exactly how far away the object reflecting the sound is. This is the principle of radar which is used to map and track the locations of aircraft in the sky and ships on the sea, in this case using electromagnetic waves. It is also the same principle used by ships that send a sonar (SOund Navigation And Ranging) pulse of sound into the ocean and ‘listen’ to...

...work. He used one of the first telescopes to discover the four largest of Jupiter's satellites and the phases of Venus. His consequent support for the theory that the Earth moves around the Sun led to his imprisonment for heresy in 1633. All the giant planets have satellites. Jupiter's four largest satellites were discovered in 1610 by Galileo Galilei (Figure 1), using...