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Planetary Motion

The Ptolemaic system , which placed the Earth at the centre of the Universe , had held sway for more than 1,500 years , from the ancient Greek era to the 16th century . But then one astronomer accurately mapped the celestial sky and carefully charted planetary motion , laying foundations for the laws of planetary motion .

" Man makes a great fuss about this planet , which is only a ball - bearing in the hub of the Universe . "


The Danish king , Frederick II , gave Brahe the small island of Heaven and provided him with funding for his work . Brahe built two great observatories there - Uraniburg and Sterneburg - equipping them with a series of extremely well - made and stable quadrants and sextants for measuring celestial positions . These were used with great care , to minimize experimental errors . Brahe showed that the comet of 1577 was further away than the Moon , measured the length of the year to an accuracy of one second , and proved that the rate of precession ( a change in direction of the Earth's rotational axis ) was not irregular . His greatest legacy was a long , accurate series of observations of the positions of the planets . These were consistently accurate to within a minute of arc ( equal to ¹ / 60 of one degree ) .

Brahe's sextant

This large floor-mounted wood and brass instrument used two sighting arms to accurately measure the distance between planets and stars that were closer than 60 degrees.

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