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| The ninth planet Pluto |
Till around 1929 the outermost planet known to man was Neptune. In 1915 the American astronomer Percival Lowell discovered that the movement of Uranus and Neptune was affected by something which axisted beyond Neptune.
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This opinion led to the search for a new planet and it was in February 1930 that an astronomer named Tombaugh discovered Pluto the ninth planet. Pluto has a diameter of out 2445 kilometres which is about one-fifth of the Earth’s and it takes 6 days and 9 hours to complete one rotation around its axis. 4497 million km away from the Sun and travelling at an average speed 4.6 kilometres per second it takes out 248 Earth’s years to complete one revolution around the Sun. It is the coldest planet in the Solar system and has a temperature of –24° centigrade and has only one moon which is approximately half its size. Pluto is so far away that from its surface the Sun is visible only as a star.
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