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.
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.
Source: Wikipedia "Nocturnal (instrument)" · CC BY-SA 4.0
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