Clock types · Time systems and signals

Time ball

Before radio, a big painted ball dropping down a mast at exactly 1 p.m. or noon was how sailors in port checked their clocks.

By David Ray · clocks.fyi

What is a time ball?

A time ball is a large ball mounted on a mast, usually on a rooftop or tower where it can be seen from the water. At a precise moment each day it is released and drops down the mast. The instant it begins to fall is the time signal.

Its main users were ship navigators. A ship's chronometer had to be accurate to work out longitude at sea, and a time ball let crews in port check it against observatory time without going ashore. Royal Museums Greenwich calls the Greenwich ball one of the world's earliest public time signals.

How it works

The routine gives watchers fair warning. At Greenwich the ball rises halfway up its mast at 12:55 p.m., reaches the top at 12:58 p.m., and drops at exactly 1 p.m. Many British time balls fell at 1 p.m. rather than noon; according to a history published by the Woods Hole Historical Museum, observatory staff were too busy working out the exact time at noon. In the United States, balls almost always dropped at noon: Boston's, for example, went to half-mast at 11:55 a.m. and to the top at 11:58 a.m.

Early balls were hoisted on a rope halyard and released by hand. Later ones used an electromagnetic release triggered by a telegraphed signal from an observatory. The Woods Hole account describes a sequence of a preliminary signal, an arming step, the time signal itself and an error signal in case of failure; in Boston, a failed drop was repeated at 12:05 p.m.

Size and height mattered. The Woods Hole ball, a metal frame covered in black canvas weighing roughly 120 pounds, was about 3.5 feet across, and it fell 25 feet from a mast top 75 feet above sea level. At Deal, Historic England records a copper ball on a 14-foot mast, rising halfway at 12:55 p.m. and to the top at 12:57 p.m. before its 1 p.m. drop.

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History

Robert Wauchope, a Royal Navy captain who later rose to admiral, promoted the idea. Smithsonian magazine reports that he began working on a visible time signal for sailors in 1818, trying flags before settling on a ball sliding down a pole. Royal Museums Greenwich credits Captain Wauchope with the first time ball, installed at Portsmouth in 1829.

Greenwich followed in 1833 with a ball on the roof of Flamsteed House at the Royal Observatory, aimed at ships on the Thames. It has an eventful past: a watercolor by Hubert Airy, son of the Astronomer Royal George Airy, shows the original wood and canvas ball lying in the courtyard after wind blew it down in December 1855; the museum notes that the exact day is uncertain. According to the Woods Hole history, more balls followed mostly between 1833 and 1845, at places including Liverpool, Mauritius, St Helena, the Cape of Good Hope, Jakarta, Valparaiso, Madras and Bombay.

The United States installed its first time ball at the Naval Observatory in Washington, D.C., in 1845. Once the telegraph spread, Western Union relayed the observatory's signal to balls in ports such as New York (1877), Boston (1879) and Philadelphia. One stood atop the U.S. Fish Commission's water tower at Woods Hole, Massachusetts, from 1885 to about 1902 or 1903.

The signals also exposed how messy local time was. Before standard time zones were adopted in the United States in 1883, noon meant local noon, which differed across the country; the railroads made a common standard necessary. In Britain, Royal Museums Greenwich notes, clocks in the east of the country ran about 30 minutes ahead of those in the west, and in 1852 the Observatory installed the Shepherd Gate Clock, the first to show Greenwich Mean Time directly to the public.

Famous examples

The Greenwich time ball still drops every day at 1 p.m. and is the most famous survivor. On the Kent coast, the Deal Timeball Tower was converted from an old semaphore station in 1855 and received its 1 p.m. signal directly from Greenwich, which worked a slave Shepherd clock that released the ball. Historic England records that it served until 1927, when wireless time signals replaced it.

The most famous descendant of the time ball is not a navigation aid at all. Smithsonian magazine notes that the first New Year's Eve ball drop in Times Square, on December 31, 1907, may have been inspired by the noon time ball on the Western Union Building in lower Manhattan, which was synchronized by telegraph with the Naval Observatory. The 1907 ball, built of iron and wood, measured five feet across and weighed 700 pounds.

See also: the world time scale that succeeded Greenwich signals on OnlineClock.app.

Why time balls disappeared

Time balls only worked for ships within sight of them, and they were only as good as the people and equipment behind them. Logged failures in the U.S. included dead batteries, broken halyards, ice, and even a broken key that kept a cover from unlocking.

New signals ended their usefulness. The Naval Observatory began transmitting daily noon time signals in 1904, and radio time signals spread quickly during World War I. Most time balls stayed in use until the 1920s. Greenwich's ball still runs as a daily tradition, and Deal's tower is now a listed building and museum.

See also: how official time reaches your phone and computer now on OnlineClock.app.

Questions people ask

Why does the Greenwich time ball drop at 1 p.m.?

British time balls commonly dropped at 1 p.m. because observatory staff were busy with their own noon observations. The Greenwich ball rises at 12:55 and falls at exactly 1 p.m. every day.

Who invented the time ball?

Captain Robert Wauchope of the Royal Navy developed the idea, and the first time ball was installed at Portsmouth in 1829. Greenwich installed its ball in 1833.

Is the Times Square ball a time ball?

Not in the original sense, but it was probably inspired by one. The first Times Square drop in 1907 may have borrowed the idea from a noon time ball on the Western Union Building in Manhattan.

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