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Transcript: A spinning top or gyroscope that has not pointed straight up will wobble. That is, its axis of rotation traces out a circle. This is called precession. The spinning Earth does exactly the same thing. It’s tilted by twenty-three and a half degrees on its axis, and the North Celestial pole traces out a large circle on the sky with a 26,000 year motion. This causes in a very subtle way the position of the North Celestial pole to change among the fixed stars. As subtle as this motion was, it is detectable by observations over many centuries and was known to ancient cultures thousands of years ago. This means that the North Celestial pole has not always pointed at the bright star Polaris. In the time of the ancient Egyptians it pointed at a different star called Thuban, and in the future the North Celestial pole will point at a different star.
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Transcript: In the year 584 B.C., on the coast of Asia Minor, two warlike tribes were engaged in a fierce battle: the Medes and the Lydains. As written by the Greek poets, these two cultures were hacking away at each other on the battlefield with burnished swords and shields, when suddenly the...
Published 07/12/11
Transcript: Thales was a philosopher who lived in the 6th century B.C. in Miletus, in what is now Turkey. No written work by Thales survives, but we know that he kept accurate eclipse records and he speculated about astronomy. He decided that the source of all things was one thing, and that...
Published 07/12/11
Transcript: The apparent motions of the stars in the night sky depend on your position on the Earth’s surface. At a northern temperate latitude, the stars rise in the east and set in the west, and they travel on slanting paths across the sky. The north celestial pole sits in the northern sky...
Published 07/12/11