Topic
nocturnal.
instrument used to determine the local time based on the relative positions of two or more stars in the night sky
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About nocturnal
A nocturnal is an instrument used to determine the local time based on the position of a star in the night sky relative to the pole star. As a result of the Earth's rotation, any fixed star makes a full revolution around the pole star in 23 hours and 56 minutes and therefore can be used as an hour hand. The 4-minute difference between the solar day and sidereal day requires a correction of this giant clock based on the date of observation, and nocturnal helps to apply this correction.
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