Time signal
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A time signal is a visible, audible, mechanical, or electronic signal used as a reference to determine the time of day.
These automatic signal clocks were synchronized by telegraphy in 1905 before the widespread use of radio
The time ball on the roof of Greenwich Observatory, London
A modern LF Radio clock
A low cost LF radio clock receiver, antenna left, receiver right.
Satellite navigation
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A satellite navigation or satnav system is a system that uses satellites to provide autonomous geopositioning. A satellite navigation system with global coverage is termed global navigation satellite system (GNSS). As of 2023, five global systems are operational: the United States's Global Positioning System (GPS), Russia's Global Navigation Satellite System (GLONASS), India's Indian Regional Navigation Satellite System (IRNSS), China's BeiDou Navigation Satellite System (BDS), and the European Union's Galileo.
The U.S. Space Force's Global Positioning System was the first global satellite navigation system and the first to be provided as a free global service.
Launched GNSS satellites 1978 to 2014