On the other hand, offset -6 doesn’t necessarily imply a time in the US. Central Standard Time (for example America/Chicago) is at offset -6, as is Mountain Daylight Time (for example America/Denver). The difference between the two will always be less than a second, so for many purposes you will not need to care. And I don’t know, but I suppose that today they (officially or in practice) define time as an offset from UTC rather than GMT.
Storing time in UTC and using UTC for transmitting date-time information is generally considered good practice. Yes, time can be captured in UTC alone.I take it that it is often used without regard to whether UTC is really intended, so don’t put too much trust into the strict definition given above. Since the world these days mostly bases precise definition of time on atomic clocks, it has become customary to base the definition of time on UTC instead.Įdit: The original meaning of GMT is somewhat useless these days, but the three letter combination doesn’t seem to go away. By contrast, in GMT the seconds are stretched as necessary, so in principle they don’t always have the same length.įor roughly 100 years GMT was used as the basis for defining time around the world. Leap seconds are inserted in UTC to keep UTC and GMT from drifting apart. In UTC a second always has the same length. UTC, which stands for Coordinated Universal Time in English, is defined by atomic clocks, but is otherwise the same. In GMT there can never be any leap seconds because Earth’s rotation doesn’t leap. Except: The Earth spins slightly unevenly, so 12 noon is defined as the annual average, mean of when the sun is at its highest, its culmination. When the sun is at its highest point exactly above Greenwich, it is 12 noon GMT. GMT stands for Greenwich Mean Time, the mean solar time at the Royal Observatory in Greenwich on the south bank in Eastern London, UK. Later GMT has become to be used at least unofficially to refer to UTC, which blurs the distinction somewhat. Although GMT and UTC are fundamentally different they are often used interchangeably because they have the same time.By the original definitions the difference is that GMT (also officially known as Universal Time (UT), which may be confusing) is based on astronomical observations while UTC is based on atomic clocks. Observations at the Royal Observatory in Greenwich halted in 1954 but it is still used, however, as the site that forms the basis for the coordinate system. Time in different time zones is calculated as an offset or difference from UTC and is expressed or written as UTC+ or UTC- the number of hours and minutes that makes the difference. Hence, leap seconds are added to keep UTC and the Earth’s rotation in line. GMT was abandoned as a standard because the Earth’s rotation is not precise and is not as exact as the atomic clocks used in the effort to keep time. While an Atomic Clock is not much use in organizing your appointments, its accuracy is paramount to systems such as mobile telephone, land line telephones, the internet, GPS, aviation programs, and digital television, where split-second precision can make the difference between failure and functionality. Therefore, they can consistently keep track of time with a minuscule error margin. But this is not the only reason Atomic Clocks are more reliable time keepers: the oscillations of the atomic nuclei are not subject to change according to factors such as power cuts, humidity or simple complacency, that would decrease the accuracy of normal clocks.
They just use the resonance frequencies of atoms as a resonator (like the pendulum your grandma’s clock). So, in a sense Atomic Clocks give the answer to the question “how accurate is accurate enough?”Ĭontrary to what you might initially believe, Atomic Clocks are not ticking bombs of nuclear destruction. However, while all of these resonators are more or less accurate, time can be subdivided almost infinitely.
Its accuracy is measured by the accuracy of the resonator at a given frequency. The need for accurate measurement of time is dire and Atomic Clocks solve this need with an error margin of 1 second to 100 million years.Ĭlocks, in general, are measuring the passage of time by counting the beat of a resonator - such as a pendulum, the oscillations of the power line or a quartz crystal. As technology advances and distances are eliminated, our lives are becoming much more fast paced.
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