Later, the era of telegraphy brought the first electronic method for time transfer in the US. Current USNO clocks are precise to about 100 trillionth of a second per day. This Cummins clock (foreground), state of the art in the mid 19th century would have cost about the same as one of Hydrogen Maser clocks in the master clock array (background) but was about one billionth as precise. A tribute to traditional time balls comes each New Year’s Eve in Times Square. Time balls, like those at Greenwich, the US Naval Observatory (USNO), and major harbors around the world, were visible by ships in the harbor and could set their on-board clocks as the ball was dropped (typically at noon). Cannon shots were one way to notify the whole fleet in harbor, but only inasmuch as the sound delay over distance could be accounted for. Time transfer was a further challenge everywhere within earshot of a cathedral or town square clock could roughly keep in step.
The mechanism for delivering standard time changed completely with the advent of radio and later satellites, but prior to the 20 th century a great many methods for keeping time were utilized: sundials, astronomic observations, zenith cameras/tubes, spring and pendulum clocks. There are still official clocks (timed from offsite sources) but those are mainly for historic and symbolic purposes. Greenwich is a fascinating place to visit and a must see for geospatial practitioners, aficionados, and the general public (who love to pose for photos straddling the meridian line). While precise timing activities are no longer performed at the Greenwich Observatory (this is now done for the UK at laboratories in the English midlands), the navigation and time meridian remains. During the era that such time-enabled navigation was developed, Britannia truly did rule the waves and established the prime meridian of this new navigation system at Greenwich Observatory, along with an official time standard (derived through astronomic observations in those days) that would become Greenwich Mean Time (GMT) – the roots of which have extended to the various subsequent time standards. Prior to time being utilized to determine longitude for global maritime commerce (and wars) and later to prevent collisions through tight scheduling for rapidly expanding rail systems, there was no compelling need for a globally synchronized time standard. Digital networks, precise navigation, transportation systems, computing, cellular networks, and the booming internet of things (IoT) are dancing to the beat of a global clock – precise to billionths of a second. But now in the digital age, our lives very much depend on (even if we do not realize it), precise time – precise almost to the point of abstraction. These tangible conventions and machinations of time – sun, moon, and stars - had served humankind well for millennia. The historic Building 1 of the United States Naval Observatoryįor all but a relatively few astronomers and scientists, the universe of humans centers around our earthbound activities and our heuristic sense of time – day, night, seasons, hours minutes, and seconds.
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