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astronomy our picture of the universe.pptx

  1. ASTRONOMY Our picture of the universe
  2. • Long,long ago,it was belived that the world is really flat plate supported on the back of gaint tortoise
  3. As long ago 340 BC the greek philoshoper Aristotle,in his book “on the heavens”was able to put forward two good arguments for beliving that the earth was a round sphere rather than a flate plate.
  4. • First Aristotle,realized that eclipses of the moon were caused by the earth coming between the sun and the moon.
  5. Second,the Greeks knew form their travels that the north star appeared lower in the sky when the viewed in the sourth than it did in more northernly.
  6. • Aristotle thought that the earth was stationery and that the sun,the moon,the planet,and the stars moved in the circular orbits about the earth • This idea was elaborated by Ptolemy in the second
  7. A simpler model, however, was proposed in 1514 by a Polish priest,Nicolas Copernicus. His idea was that that the sun was stationery at the centre and that the earth and the planets moved in circular orbits around the sun. Galileo Galilei started publicly to support the copernican theory.
  8. • When he looked at the planet jupiter, Galileo found that it was accompaniedby several small satellites or moon that orbited around it. This implied that everything did not have to be in orbit directly around the earth, as Aristotle and Ptolemy had tought. • In 1609,Galileo Galilei started observing the night sky with a telescope, which had just been invented
  9. • An explanation was provided only much later, in 1687, when sir Issac Newton published his “philosophiae Naturalis Principia Mathematica”in which he not only put forward a theory of how bodies move in space and time but also developed the complicated mathematics needed to analyse those motions.
  10. • In addition Newton postulated a law of universal gravitation according to which each body in the universe was attracted toward every other body by a force that was stronger,the more massive the bodies and the close they were to each other.
  11. • Later in 1929, Edwin hubble made the landmark observation that whatever you look distant galaxies are moving rapidly away from us. • In other word universe is expanding. This means that a earlier times objects would have been closer together. • Infact it seemed that there was a time, about ten or twenty thousand million year ago, when they were all at exactly the same place when, therefore the density of the universe was infinite. • This discovery finally brought the question of the beginning of the
  12. Hubbles observations suggested that there was a time, called the Bigbang, when the universe was infinitesimally small and infinitely dense under sucjh condition all the laws of science, and therefore all ability to predict the future, would break down.
  13. In short, the Big Bang hypothesis states that all of the current and past matter in the Universe came into existence at the same time, roughly 13.8 billion years ago. At this time, all matter was compacted into a very small ball with infinite density and intense heat called a Singularity.
  14. Our solar system began to form around 5 billion years ago, roughly 8.7 billion years after the Big Bang. A solar system consists of a collection of objects orbiting one or more central stars. All solar systems start out the same way. They begin in a cloud of gas and dust called a nebula .
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