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Transcript
Sidereal and Solar Time We measure time according to the position of the Sun in the sky. o Our day is the time from Noon to Noon and is exactly 24 hours long. This time period is called a ``Solar Day''. It takes the Earth 23 hours 56 minutes and 4 seconds to complete a rotation. o This time period is called the ``Sidereal Day.'' o During the course of a day the Earth travels a short distance in its orbit around the Sun. After the Earth has completed one rotation the Earth must turn for an extra 4 minutes in order to bring the Sun back to the same point in the sky. The time from Noon to Noon (the Solar Day) is longer than the true rotation period of the Earth (Sidereal Day) by about 4 minutes as a result. The stars rise and set on a Sidereal schedule. A star or constellation will be at precisely the same position in the sky 4 minutes earlier with each successive day. The sidereal time at any given location (Celestial Meridian) on earth is the same as the right ascension at that point.