A time ball is a large painted wooden or metal ball that drops at a predetermined time, principally to enable sailors to check their marine chronometers from their boats offshore. Accurate timekeeping is one way of enabling mariners to determine their longitude at sea.
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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 Meantime 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.[2] Others followed in the major ports of the United Kingdom (including Liverpool) and around the maritime world.[2] 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.[3] Wauchope submitted his scheme to American and French ambassadors when they visited England.[2] The US Naval Observatory was established in Washington D.C. and the first American time ball went into service in 1845.[2]
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.[4]
With the commencement of radio time signals (in Britain from 1924), time-balls gradually became obsolete and many were demolished in the 1920s.[5]
Today there are over sixty time balls standing, though many of these are no longer operational. The existing stations include those at:
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[7] and a decision was made in March 2011 to dismantle the building due to the danger it posed to the public.[8] The tower collapsed during the major aftershock which hit the Lyttelton area on 13 June 2011.[9]
A modern variant on the time ball is the ball drop on New Year's Eve, notably in Times Square, New York City. Unlike a standard time ball, where the drop starts at exactly noon or 1 p.m., the Times Square drop starts at 11:59:00pm on December 31 and completes 60 seconds later at midnight on January 1. When a leap second was observed at the end of 1987, the drops lasted 61 seconds with the countdown being ... 5, 4, 3, 2, 1, Leap Second, Zero.[10] (At the time, the leap second was added at local time; since 1988, leap seconds have been appended worldwide at midnight UTC.)