![]() ![]() This format has advantages such as being largely unambiguous, easy to parse by machine, easy to read by humans across cultures. The T separates the date portion from the time-of-day portion. For a date-time the format YYYY-MM-DDTHH:MM:SS±HH:MM:SS is used. ISO 8601įurthermore, best practice in formatting date-time textually for computing is to us the ISO 8601 standard formats. ZuluĪs a shortcut for an offset of zero, the letter Z is commonly used to mean UTC itself. The leading zero and the colon are both optional but I have seen libraries break when encountering a value such as -0800 or -8. The best in practice is with both hours and minutes along with a colon, such as +00:00, +05:30, or -08:00. To write that string with an offset, various conventions may be applied. If the string is meant to represent a moment at UTC itself, that means an offset-from-UTC of zero. If a string indicates a specific moment, it must indicate either a time zone ( Continent/Region formatted name) and/or an offset-from-UTC as a number of hours-minutes-seconds. That first part is a bad example, with the date-time string lacking an indicator of its offset or zone. Here is some more practical advice, with code examples. So for all practical purposes in most apps, no difference at all. You can use the terms interchangeably, with the difference being literally less than a second. ![]() correctly summarizes the technical differences - for details follow the links to detailed pages in Wikipedia.įor programmers building business-oriented apps, the upshot is that UTC is the new GMT. ❌ The accepted Answer is neither correct nor useful. Current Millis with a simple and a complex take on UTC vs.I don’t think you got your example time exactly right, but yes, 2 January 2018 at 00:00 UTC is the same point in time as 1 January 2018 at 18:00 in Chicago and other places that are at UTC-6 in winter (winter on the Northern hemisphere, that is).Parts of Canada and Mexico use it too, of course, and also Galapagos and Easter Island. 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. I suppose it’s up to each state of the US to define its time.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. Next time change is highlighted.ĭata for the years before 1970 is not available for Bellevue, however, we have earlier time zone history for Los Angeles available.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. The graph above illustrates clock changes in Bellevue during 2023.ĭaylight Saving Time (DST) changes do not necessarily occur on the same date every year. Business Date to Date (exclude holidays). ![]()
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