UTC is the time at the Prime Meridian (0 Longitude) given in hours and minutes on a 24 hour clock. The various flavours of Universal Time are about astronomical timekeeping.Īnd civil timekeeping, I think, was what the original question was about. UTC use to be called Greenwich Mean Time (GMT), but still is in English speaking countries, or Zulu Time (Z), which is used in plane and ship navigation. It is enshrined in law in the UK, Ireland, Canada, even Belgium. GMT is about civil timekeeping in English-speaking countries. If you are concerned about hours, not seconds, you probably won't care. But you need an astronomer to explain the difference to you. For the past 80 years the terms GMT and Universal Time have been almost synonymous. Its point was that, before 1925, GMT was counted from noon not midnight, so even though it was 10 years later, the possibility of ambiguity might still have then persisted. This advice, from the International Astronomical Union, dates back to 1935. One respondent has said one should use UTC in preference to GMT. Europeans generally do not talk about "daylight time" but "summer time", at least in the languages I know.
In the real world, in winter the UK observes GMT (Greenwich Mean Time) and in summer it observes BST (British Summer Time).
Utc time vs gmt windows#
They are mythical animals that appear only in the bestiary called the Windows Registry. The names GMT Standard Time and GMT Daylight Time are unknown outside of Redmond. This is a late response that the original questioner is unlikely to read but which people who google for this topic may find. It may have times that are very similar to UTC for half of the year but that is all! I feel fairly confident that this timezone definition (whatever it should be called) is not UTC. If you strictly go by the definition of what UTC and GMT are, there is no real practical. For computers, GMT is UTC+0 so they are the equivalent. One is measured from the sun and another from an atomic clock. They obviously wanted to describe the timezone in use in UK/Ireland but they gave it an ID that included the terms "GMT" and UTC in the ID and the display name. UTC is an atomic time scale which only approximates GMT with a tolerance of 0.9 second.
It seems (at least to me) that whoever was in charge of defining timezones in Microsoft has really muddied the waters even further here.
I was very surprised to see the following definition of the "GMT Standard Time" timezoneĭisplay Name: (UTC) Dublin, Edinburgh, Lisbon, Londonĭaylight Name: GMT Daylight Time ***Has Daylight Saving Time***īegins at 01:00 on Sunday of week 5 of MarchĮnds at 02:00 on Sunday of week 5 of October
Utc time vs gmt code#
To confuse things even more, I ran the sample code from the MSDN docs for TimeZoneInfo.GetSystemTimeZones and looked at the output. There seems to me to be a confusion over the use of the term "GMT" which seems to be used to mean "Greenwich Mean Time" and also the timezone used in the UK/Ireland - which flips between GMT in winter and British Summer time in summer and doesn't seem to have a well defined name in its own right!
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