I certainly believe it belongs here. Another factoid regarding time. Add a comment. Active Oldest Votes. Astronomy versus Atomic clock 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.
For your questions: Yes, time can be captured in UTC alone. The difference between the two will always be less than a second, so for many purposes you will not need to care.
Further reading: Systems of Time. Current Millis with a simple and a complex take on UTC vs. Improve this answer. Ole V. This is why i downvoted: This answer is wrong please read here: currentmillis. Historically you are correct but no longer the case — JohnChris.
Don't delete the link, it works sorry i edited my comment. Thanks, JohnChris, for trying to explain the downvote. I will delete the broken link, thank you. Here is some more practical advice, with code examples.
ISO Furthermore, best practice in formatting date-time textually for computing is to us the ISO standard formats. Instant Always in UTC. Technically, a count of nanoseconds since the epoch reference of first moment of TZ. OffsetDateTime A date with time-of-day in the context of a certain number of hours-minutes-seconds ahead of, or behind, UTC. ZonedDateTime A date with time-of-day in the context of a certain time zone. Back to your example in your point 3, let's look at some code.
Not a moment First, we parse your input string. So correct the faulty text input by assigning the context of an offset of zero, for UTC itself. About java. Where to obtain the java. Java 9 adds some minor features and fixes. Android Later versions of Android bundle implementations of the java. Basil Bourque Basil Bourque k 75 75 gold badges silver badges bronze badges.
Thanks a lot. IMHO this is one of the best comments on the issues of date-time-related programming. Minor note that has indeed caused major headaches nonetheless if ignored "sorting alphabetically is also chronological" is only true if subsecond times are ignored.
In general I've found things like SS. The accepted answer is correct. GMT is a timezone though and thats the only difference, which the accepted answer specifies. Please fix your answer as to not spread misinformation — JohnChris. JohnChris The offset of a time zone can change at the whim of politicians. GMT never changes. As I said in the Answer, a time zone is a history of the past, present, and future changes to the offset used by the people of a particular region.
UTC is not a time zone, but a time standard that is the basis for civil time and time zones worldwide. This means that no country or territory officially uses UTC as a local time.
JPS 2, 5 5 gold badges 26 26 silver badges 53 53 bronze badges. Abdullah Ahmed Ghaznavi Abdullah Ahmed Ghaznavi 1, 3 3 gold badges 15 15 silver badges 25 25 bronze badges. GMT is the old-school marker for defining offsets around the world.
We must pick some arbitrary spot on earth so as to say all other spots are a certain number of hours-minutes-seconds ahead or behind that. GMT is not a time zone, it is the measure by which all other time zones are measured. A time zone is the history of past, present, and future changes to the offset-from-GMT now UTC used by the people of a particular region.
You can check tz database to ensure: en. The difference is kept under a second using leap seconds but that can still be critical in some cases so this answer is bad. GrixM you are wrong, historically you are correct, but with a bit of research you will find that the accepted answer is correct. BasilBourque you are wrong, historically you are correct, but with a bit of research you will find that the accepted answer is correct.
Show 5 more comments. The name derives from the place where the solar time was standardised for everyone: it was established at The Royal Observatory Greenwich. Also, considering that each day requires the same interval, the pendulum clocks at the observatory was the perfect mechanism to standardise time for the universal coordination.
Although the abbreviation does not match the term, it was used as a compromise for the translation from European languages. To calculate the UTC time, the atomic clocks with frequency cycles are used to display the accurate measurements of time. The history of GMT started with the decision of the International Meridian Conference in to establish the prime meridian which would denote the international standard of time. Considering that Great Britain was a developed marine nation, it used Greenwich Meridian to position own ships.
Subsequently, Greenwich meridian was determined as zero degrees longitude, thus, the international standard time 2. From that point, every nation used GMT to calculate the time in relation to this standard. Eventually, GMT became the unified standard for the economic interactions between countries around the world.
The advancement of the technologies of the wireless telegraph indicated that all countries require precise time standard. As a result, in , the International Congress on Astronomical Ephemerides agreed to use GMT for the universal offset of the clocks for other nations.
In , the concept of UTC was established as the primary international standard which would denote how other countries would regulate their time in relation to UTC 3. The primary reason why UTC was considered to be a more accurate system was the fact that it used the rotation of Earth and atomic clocks for measurements. Source: Wikipedia. However, since , TAI adds one leap second every 19 months.
The positive tendency of the leap second in time reflects that the Earth slows down its rotation 4. However, you need to know what happens during daylight saving time in the United States. In short, the local time is advanced one hour during daylight saving time. As an example, the Eastern Time zone difference from UTC is -4 hours during daylight saving time rather than -5 hours as it is during standard time.
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