FACTOID # 21: 15% of Army recruits from South Dakota are Native American, which is roughly the same percentage for female Army recruits in the state.
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Encyclopedia > Time ball
The timeball at Greenwich is shown in the top right of picture
The timeball at Greenwich is shown in the top right of picture

A time ball is a large metal or painted wooden 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 at sea. Royal Observatory, Greenwich Image by ChrisO File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... Royal Observatory, Greenwich Image by ChrisO File history Legend: (cur) = this is the current file, (del) = delete this old version, (rev) = revert to this old version. ... 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. ... Map of Earth showing lines of longitude, which appear curved and vertical in this projection, but are actually halves of great circles 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. ...

Time ball stations set their clocks according to transit observations of the positions of the sun and stars. 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 manually to observatory time. Through the use of the electric telegraph (from around 1850), time balls could be located at a distance from their source of Mean Time and operated remotely.

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.

The first time ball was erected at Portsmouth in 1829 by its inventor Robert Wauchope, a Captain of the Royal Navy. 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. 1833 was a common year starting on Tuesday (see link for calendar). ... Royal Observatory, Greenwich The original site of the Royal Greenwich Observatory (RGO), which was built as a workplace for the Astronomer Royal, was on a hill in Greenwich Park in Greenwich, London, overlooking the River Thames. ...


Today there are over 60 time balls standing, including those at the Greenwich Observatory, Edinburgh, Point Gellibrand, USA, Deal, Kent. A modern version of a time ball is dropped at the stroke of midnight on December 31, notably in Times Square, New York City. Location within the British Isles Deal is a town in Kent, England. ... Times Square Times Square is also the name of a station on the Detroit People Mover, a shopping mall in Hong Kong, and a 1980 movie. ... New York City, officially named the City of New York, is the most populous city in the United States, the most densely populated major city in North America, and the largest financial center in the world. ...

See also

A time signal is a visible, audible, mechanical, or electronic signal used as a reference to determine the time of day. ...


Time Ball Tower Museum

  Results from FactBites:
Time signal - Wikipedia, the free encyclopedia (1023 words)
When more accurate public time signals were desired for use in navigation, a number of traditional audible or visible time signals were established for the purpose of allowing navigators to set their chronometers by.
The ball was set to drop at 1 P.M. to enable the astronomers to establish the correct moment it should drop by observing the sun at noon.
Loran-C time signals may also be used for radio clock synchronization, by augmenting their highly accurate frequency transmissions with external measurements of the offsets of LORAN navigation signals against time standards.
  More results at FactBites »



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