time-ball
Noun: A time-ball is a visual time signal device. It consists of a large, often brightly colored ball mounted on a pole or staff. At a precise, predetermined time each day (traditionally noon), the ball is released to slide or drop down the staff. This drop provides a clear, visible signal to ships in a harbor and people in the vicinity, allowing them to accurately set their marine chronometers and other timepieces.
The time-ball was historically a critical tool for maritime navigation before the widespread use of radio time signals. Its primary function was to disseminate accurate time from an observatory or time-keeping institution.
- The sailors watched for the time-ball to drop at the observatory to calibrate their ship's clock.
- The Greenwich time-ball has been operational since 1833.
- With the advent of wireless telegraphy, the importance of the time-ball diminished.
- As a historical landmark: Many former time-ball stations are now preserved as historical monuments.
- The restored time-ball on top of the old customs house is a popular tourist attraction.
- Time signal (n): A broader term for any indication of the exact time (audible, like a time pips, or visual, like a time-ball).
- Chronometer (n): A precise, portable timekeeper used for navigation, which would be set using a time-ball signal.
- Visual time signal
- Time-drop (less common)
The time-ball is a specific type of time-signaling apparatus. It is not used in general language to refer to any ball used in games or sports. Its usage is almost exclusively historical or technical in the context of horology (the study of timekeeping) and maritime history.
- a ball that slides down a staff to show a fixed time; especially at an observatory