Noun
time ball (plural time balls)
A large wooden or metal ball that drops at a predetermined time to enable sailors to check their marine chronometers from their boats offshore.
time-ball (plural time-balls)
Rare spelling of time ball.
time ball
To help others synchronise their clocks to GMT, Astronomer Royal John Pond had a time ball installed atop the observatory in 1833. Source: Internet
The time ball was dropped every day except Sunday precisely at the astronomically defined moment of Mean Solar Noon, enabling all ships and civilians to know the exact time. Source: Internet
Hourly time signals from Greenwich Observatory were first broadcast on 5 February 1924, rendering the time ball at the observatory redundant in the process. Source: Internet
It was the first time ball in the United States, being placed into service in 1845, and the 12th in the world. Source: Internet