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mercury venus mars jupiter and saturn were well -know in ancient times because they can be easily seen sen with the nakedeye and their movements are easily differentiated from stars which are fixed position .
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suggested that the earth revolved around the sun .
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classified the stars according to their apparent brightness
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published his heliocentric miodel according to which the planets revolved around the sun
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carried out very detailed observation of the planets
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used the telescope for the first time to observe the sky
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built the first telescope using mirrors instead of lenses
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his book the principles of natural philosophy in which he explained the laws governing the moment of the planets
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explaind newtons laws and predicted the turn of the comet in 1758
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discovered the planet uranus
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measured the distence from a star for the first time using geometric geometric
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lead to discover neptune
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proved that some of the nebulas seen in the sky are in fact independent galaxies
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discovered pluto
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the discovery of the firts extra-solar planets
