A time ball is an obsolete time signalling device. It consists of a large, painted wooden or metal ball that is dropped at a predetermined time, principally to enable navigators to verify their marine chronometers from their ships offshore. Accurate timekeeping is one means by which longitude can be determined at sea.
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. Following the introduction of the electric telegraph around 1850, time balls could be located at a distance from their source of mean time and operated remotely.
The first time ball was erected at Portsmouth, England in 1829 by its inventor Robert Wauchope, a Captain in the Royal Navy. Others followed in the major ports of the United Kingdom (including Liverpool) and around the maritime world. One was installed in 1833 at the Greenwich Observatory by Astronomer Royal John Pond, and the time ball has dropped at 1 p.m. every day since then. Wauchope submitted his scheme to American and French ambassadors when they visited England. The US Naval Observatory was established in Washington D.C. and the first American time ball went into service in 1845.
Time balls are usually dropped at 1 p.m. (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 was recorded when the ball began descending, not when it reached the bottom.
Time balls around the world 
Today there are over sixty time balls standing, though many of these are no longer operational. The existing stations include those at:
- Deal, Kent
- The Old Windmill, Brisbane, Australia
- Fremantle, Western Australia
- Gdańsk, Poland (The time ball was installed in 1876, moved to the Danzig (now Gdańsk) lighthouse in 1894, and removed in 1929. In 2008 it was reconstructed from original plans)
- Greenwich Observatory
- Clock Tower, Brighton, East Sussex (originally operated hourly, but was later stopped as it was too noisy)
- Nelson's Monument on Calton Hill, Edinburgh
- Point Gellibrand, Victoria
- Sydney Observatory, Australia
- Victoria & Alfred Waterfront, Cape Town
- United States Naval Observatory
- Titanic Memorial, New York
- Citadelle of Quebec, Quebec City
- Semaphore, South Australia
Lyttelton Timeball Station 
The Lyttelton Timeball Station in Lyttelton, New Zealand was operational until it received partial damage in the 2010 Canterbury earthquake. Further severe damage occurred in the February 2011 Christchurch earthquake and a decision was made in March 2011 to dismantle the building due to the danger it posed to the public. The tower collapsed during the major aftershock which hit the Lyttelton area on 13 June 2011. In November 2012 a large financial donation  was made available to contribute towards rebuilding the tower and is being considered by the community.
Times Square 
A modern variation on the time ball has been used since 1908 for New Year's Eve celebrations at New York City's Times Square, where a lit crystal ball located on a pole atop One Times Square is lowered to signal midnight and the arrival of the new year. Unlike a typical time ball, where the beginning of its descent is used as the time signal, the ball begins to be lowered one minute prior at 11:59 p.m., completing its descent at the bottom of the pole at midnight. For 1988, the event's organizers acknowledged the addition of a leap second at midnight by extending the drop to 61 seconds (at the time, the leap second was added at midnight local time, Since 1988, leap seconds have been appended worldwide at midnight UTC, which is five hours before midnight in New York.)
See also 
- Blackhead Point, in Hong Kong, where a time ball was operated from 1908 to 1933
- History of longitude
- Shepherd gate clock
- Time signal
- Weather ball
- "Lyttelton Timeball Station, Christchurch". Yahoo! Travel.
- Aubin, David (2010). The Heavens on Earth: Observatories and Astronomy in Nineteenth-Century Science and Culture. Durham, N.C.: Duke University Press. p. 164. ISBN 978-0-8223-4640-1.
- Greenwich Time Ball Retrieved December 27, 2010
- "Deal Timeball Tower: The Ball Drop". Retrieved 4 January 2009.
- "The Gdańsk Nowy Port Lighthouse and Time Ball". Retrieved 4 January 2009.
- "Heritage Gateway Listed Buildings Online — Clock Tower and Attached Railings, North Street (north side), Brighton, Brighton and Hove, East Sussex". Heritage Gateway website. Heritage Gateway (English Heritage, Institute of Historic Building Conservation and ALGAO:England). 2006. Retrieved 2 June 2010.
- "New Zealand quake: The epicentre town". BBC News. 25 February 2011.
- Gates, Charlie (4 March 2010). "Timeball Station to be demolished". stuff.co.nz. Retrieved 15 June 2011.
- Greenhill, Marc (14 June 2011-updated). "Workmen unscathed as Timeball Station collapses". stuff.co.nz. Retrieved 15 June 2011.
- Greenhill, Marc (28 November 2012). "Donor fronts to save Lyttelton Timeball Station". Stuff. stuff.co.nz. Retrieved 2012-11-28.
- McFadden, Robert D. (1987-12-31). "'88 Countdown: 3, 2, 1, Leap Second, 0". New York Times. Retrieved 2 January 2009.
- "NYC ball drop goes 'green' on 100th anniversary". CNN. December 31, 2007. Retrieved 2007-12-31.
- "List of Timeballs". Index to the House Documents, Otherwise Publ. as Executive Documents. U.S. Congress. 1876-1877. pp. 305–308. List of time balls worldwide in 1876.
- Time ball/cannon hobbyist
- Time ball and cannon Association
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