Time ball

A time ball is a large metal ball, visible to shipping, that drops at a predetermined time to enable sailors to set their chronometers. Accurate timekeeping is important in enabling sailors to determine their longitude.

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Time balls were used before the days of radio, and in particular the time signals and announcements. Time ball stations would set their clocks according to readings of the positions of the sun and stars from observatories. Originally they either had to be stationed at the observatory itself, or had to keep a very accurate clock at the station which was set according to an observatory, or in latter years from signals carried by the telegraph system.

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Time balls are usually dropped at 1pm (although in the USA they were dropped at noon). They were raised half way about 5 minutes earlier to alert the ships, then with 2-3 minutes to go they were raised the whole way. The time ball was not usually dropped at noon as the observatories would be too busy taking readings.

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The first time ball was erected in Manchester, at their observatory. Others followed in the major ports of the UK and around the maritime world. One was installed in 1833 at the Greenwich Observatory, and has dropped at 1pm every day since then. They gradually became obsolete and many were demolished in the 1920s.

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Chronometer: A chronometer is a clock designed to have sufficient long-term accuracy that it can be used as a portable time standard on a vehicle, usually in order to determine longitude by means of celestial navigation. In Switzerland, only timepieces certified by the COSC may use the word 'Chronometer' on them...

Longitude: Longitude, sometimes denoted by the Greek letter λ, describes the location of a place on Earth east or west of a north-south line called the Prime Meridian. Longitude is given as an angular measurement ranging from 0? at the Prime Meridian to +180? eastward and −180? westward. Unlike la...

Radio: Radio is the wireless transmission of signals, by modulation of electromagnetic waves with frequencies below those of light....

Time ball related Images and Photos (experimental)

Privates Daly Ball and Baldwin Testing Out Burro by Riding Him at Same Time	Time	Ball I	Time's Up
Ball IV	Ball II	Ball III	Time Code
Ball Four: Soccer	Ball Four: Football	Ball Four: Baseball	Time Flies