The red Time Ball, positioned on top of Flamsteed House is one of the world's earliest public time signals, distributing time to ships on the Thames and many Londoners. It was first used in 1833 and still operates today.

The Time Ball was made by Maudslay, Son & Field and is controlled by a mechanism inside the north-eastern turret. The ball drops at 1:00 PM daily (this is 1:00 PM British Summer Time when BST is in operation).

By the 1830s, most British sailors navigated using chronometers. These needed to be set accurately before sailing, and the Time Ball allowed anyone in sight of the Royal Observatory to obtain Greenwich Time.

On 6 December 1855, a winter gale blew down the time ball from the roof of the Observatory into the Courtyard.

Originally the ball was raised by a hand-operated winch and released by an Observatory assistant looking at the dial of an accurate clock. In 1852 the release was automated and was carried out by an electric impulse from the Shepherd Master Clock.

In the 1950s, the raising mechanism was replaced by an electric motor. The time now comes from a computer clock reset by the national radio time signal controlled by the National Physical Laboratory.