Time ball

Common card · No. 357353

A time ball is a large, wooden or metal ball that moves up and down a pole, and which is dropped at a predetermined time of day. Because precise timekeeping is essential to the determination of longitude at sea, time balls were principally erected to allow navigators aboard nearby ships to synchronize their marine chronometers with a reference time standard controlling the ball. Time balls have been rendered obsolete by electronic time signals, but some are kept in operation as tourist attractions.

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