Editing Royal Observatory, Greenwich (section)

===Greenwich Time Ball===
[[File:London, Greenwich, Royal Greenwich Observatory -- 2016 -- 4695.jpg|thumb|The [[time ball]] is the red ball on a post – when it drops a certain time is signalled. This allowed clocks to be set from afar with great accuracy, particularly the [[Marine chronometer|chronometers]] of ships on the [[River Thames]] below, prior to sailing. The observatory would first determine the time by stellar observations.]]
The red [[time ball]] of Greenwich was established in 1833, and is noted as a public time signal.<ref name="rmg.co.uk">{{cite web | url=https://www.rmg.co.uk/see-do/we-recommend/attractions/see-time-ball-drop | title=The Greenwich Time Ball }}</ref> The time ball in modern times is normally in a lowered position, then starting at 12:55{{nbsp}}pm, the ball begins to rise, then at 12:58 it reaches the top; at 1{{nbsp}}pm the ball drops.<ref name="rmg.co.uk"/>

To help mariners at the port and others in line of sight of the observatory to synchronise their clocks to GMT, Astronomer Royal [[John Pond]] installed a very visible time ball that drops precisely at 1{{nbsp}}pm (13:00) every day atop the observatory in 1833. Initially it was dropped by an operator; from 1852 it was released automatically via an electric impulse from the [[Shepherd Gate Clock|Shepherd Master Clock]].<ref>{{cite web |url=http://londonist.com/2009/12/from_the_royal_observatory_the_gree |title=From The Royal Observatory: The Greenwich Time Ball |newspaper=Londonist.com |date=  9 December 2009}}</ref> The ball is still dropped daily at 13:00 (GMT in winter, [[British Summer Time|BST]] in summer).<ref>{{cite web|url=http://wwp.greenwichmeantime.com/info/timeball.htm|title=Greenwich Time Ball}}</ref>

The original time ball system was built by Messrs Maudslay and Field, and cost £180.<ref name="Laurie-1958">{{Cite journal|title=1958Obs....78..113L Page 113|journal = The Observatory|volume = 78|pages = 113|bibcode = 1958Obs....78..113L|last1 = Laurie|first1 = P. S.|year = 1958}}</ref> The five-foot diameter ball was made of wood and leather.<ref name="Laurie-1958"/> In the original ball system, it was hoisted by a rope up from the Octagon room, and there was a catch at the top to hold it.<ref name="Laurie-1958"/> This could then be triggered by hand, while observing the time on an astronomical month clock, that was regulated to the [[mean solar time]].<ref name="Laurie-1958"/>

By dropping the ball, the public, mariners, and clock makers could then get a time signal by viewing it from afar.<ref name="Laurie-1958"/> The ball drop would be repeated at 2{{nbsp}}pm also if possible.<ref name="Laurie-1958"/>

The reason why 12 noon was not chosen was because astronomers at the observatory would record when the Sun crossed the meridian at that time on that day.<ref>{{Cite book|url=https://books.google.com/books?id=ygJCDwAAQBAJ&q=greenwich+time+ball&pg=PA61|title=Marine Chronometers at Greenwich|last=Betts|first=Jonathan|date=2018-01-04|publisher=Oxford University Press|isbn=9780199641383|language=en}}</ref>

In rare occasions where the ball could get stuck due to icing or snow, and if the wind was too high it would not be dropped.<ref name="Laurie-1958"/><ref>{{Cite book|url=https://books.google.com/books?id=adA0AQAAMAAJ&q=greenwich+time+ball&pg=RA2-PA15|title=Observations Made at the Royal Observatory, Greenwich in the Year ... in Astronomy, Magnetism and Meteorology|date=1921|publisher=H.M. Stationery Office|language=en}}</ref> In 1852, it was established to distribute a time signal by the telegraph wires also.<ref name="Laurie-1958"/>

The time ball was extremely popular with the public, chronometers, railways, mariners, and there was a petition to have another time ball established in [[Southampton]] also.<ref name="Laurie-1958"/>