Time signal

A time signal is a visible, audible, mechanical, or electronic signal used as a reference to determine the time of day. Church bells or voices announcing hours of prayer gave way to automatically operated chimes on public clocks; however, audible signals (even signal guns) have limited range. Busy seaports used a visual signal, the dropping of a ball, to allow mariners to check the chronometers used for navigation. The advent of electrical telegraphs allowed widespread and precise distribution of time signals from central observatories. Railways were among the first customers for time signals, which allowed synchronization of their operations over wide geographic areas. Dedicated radio time signal stations transmit a signal that allows automatic synchronization of clocks, and commercial broadcasters still include time signals in their programming. Today, GPS navigation radio signals are used to precisely distribute time signals over much of the world. There are many commercially available radio controlled clocks available to accurately indicate the local time, both for business and residential use. Computers often set their time from an Internet atomic clock source. Where this is not available, a locally connected GPS receiver can precisely set the time using one of several software applications. One sort of public time signal is a striking clock. These clocks are only as good as the clockwork that activates them, but they have improved substantially since the first clocks from the 14th century. Until modern times, a public clock such as Big Ben was the only time standard the general public needed. Accurate knowledge of time of day is essential for navigation, and ships carried the most accurate marine chronometers available, although they did not keep perfect time. A number of accurate audible or visible time signals were established in many seaport cities to enable navigators to set their chronometers. In Vancouver, British Columbia, a '9 O'Clock Gun' is still shot every night at 9 pm. (This gun was brought to Stanley Park in 1894 by the Department of Fisheries originally to warn fishermen of the 6:00 pm Sunday closing of fishing.) The 9:00 pm firing was later established as a time signal for the general population. Until a time gun was installed, the nearby Brockton Point lighthouse keeper detonated a stick of dynamite. Elsewhere in Canada, a 'Noon Gun' is fired daily from the citadels in Halifax and Quebec City. In the same manner, a noon gun has been fired in Cape Town, South Africa, since 1806. The gun is fired daily from the Lion Battery at Signal Hill. A cannon was fired at one o'clock every weekday at Liverpool, England, at the Castle in Edinburgh, Scotland, and also at Perth in Australia to establish the time. The Edinburgh 'One O'Clock Gun' is still in operation. A cannon located at the top of Santa Lucia Hill, in Santiago, Chile, is shot every noon.