8

If I do a Google Search for "Time zone Ulaanbaatar", I get, inter alia,

Ulaanbaatar Time Zone UTC+08:00

However, if I do "Time in Ulaanbaatar", I get

10:42 am
Sunday, 21 August 2016 (GMT+9)
Time in Ulaanbaatar, Mongolia

Why do I get 8 hours for one result, and 9 hours for the other one?

  • In short, daylight saving time. Note that results for e.g. New York return the correct time at the expense of assigning the city to EDT, which is (arguably) not actually a time zone. – E.P. Aug 21 '16 at 12:26
  • I'm voting to close this question as off-topic because it's not about travel. – JonathanReez Aug 22 '16 at 9:01
10

It is mostly correct to say that the time zone of Ulaanbaatar is UTC+8. However, saying that is a shortcut, because a timezone is a geographical place with a certain rules regarding time, and UTC+8 is a time offset. A lot of timezones also observe daylight saving time (DST) in the summer, which adds another offset in the same timezone.

Let's use another example. A lot of places, like my home in Montreal, or most of North America and Europe, are in timezones with two offsets: one without DST, and one with DST, one hour later. So the North American East coast, in Eastern Time timezone, will observe Eastern Standard Time (EST) in the winter, UTC–5, and Eastern Daylight Time (EDT) in the summer, at UTC–4.

Since, at the time of your question and this answer, it is currently summer in the Northern hemisphere, Mongolia is (as of August) in DST, and thus one hour later than their standard offset of UTC+8 (winter), hence UTC+9. And indeed, if you consult Wikipedia at Time in Mongolia, you'll see Ulaanbaatar's two offsets.1

It might be helpful to know that since UTC is used as the standard for time and is based on the rotation of the earth, it needs to be an absolute reference and can't change with daylight time. That means that the other offsets will have to change around it. (It comes in handy when a timezone changes the date it wants to observe DST, for instance.—And GMT is just the old standard before UTC.)


1 Usually, you can also consult the page for the city which will also mention the two offsets, but as you've discovered, I understand Mongolia has introduced DST recently so Wikipedia might not be up to date on all pages yet.

* Special thanks to commenters DJClayworth, Tom, and Bakuriu, who rightly pointed out that a timezone and an offset is not the same thing. This answer was corrected to use the proper terminology.

  • 3
    People don't normally say "Montreal has two timezones", they would say that in the timezone of Montreal the offset from UTC is different in summer and winter. – DJClayworth Aug 21 '16 at 2:34
  • Officially there is one time zone, Eastern (using your Montréal example). The Daylight Time is simply a localized adjustment of clocks within the Eastern Time Zone, not a second time zone. Standard Time is the universally designated time for the zone. – user13044 Aug 21 '16 at 3:08
  • I think this answers gets something wrong, or at the very least the explanation is confusing. Also you claim that Ulaanbaatar has two different time zones, but if you look at the file mentioned in wikipedia zone.tab you see that the time zone is one and there is a DST offset during summer. – Bakuriu Aug 21 '16 at 12:54
  • Thanks folks, I've updated the words to be more correct. I'll probably revisit the structure eventually to make it clearer. – Jonathan Allard Aug 22 '16 at 4:48
  • 1
    @Tom standard time is the time that is in effect in the winter. People often say "Eastern Standard Time" in the summer, but they are wrong to do so. – phoog Aug 23 '16 at 16:40
2

I don't understand the difference between UTC or GMT, or the difference between asking about the time in a place and a place's time zone, but Mongolia re-introduced daylight saving time in 2015, and it's still in use this year. From Mongolia to go into daylight saving time this month by B.Khuder:

Ulaanbaatar /MONTSAME/ In accordance with the cabinet resolution, the time zones of Mongolia will transmit into the daylight saving time.

The time zones will go into the summer time at 12.00 am on March 25. It means that all in Mongolia must adjust their clocks forward one hour close to the start of spring and adjust them backward in the autumn to the standard time, so the evening daylight is experienced an hour longer. The period of summer time will continue until September 30.

Mongolia observes two time zones, the west Mongolia observes UTC +7, while the central and east--UTC +8. The country abolished the use of daylight saving time in 2007, but restarted it in March of 2015.

  • 2
    GMT (Greenwich Mean Time) is the older zero point for time that was based on the rotation of the earth, whereas UTC (Coordinated Universal Time) is a newer system based on atomic clocks. GMT is a designated time zone, UTC is not, rather it is a scientific reference value (but mistakenly appears on some maps as a time zone). Both have the same time value. – user13044 Aug 21 '16 at 2:17
  • For travel purposes and flight planning, only UTC is used, not GMT. – Burhan Khalid Aug 21 '16 at 7:06
  • GMT (or, strictly speaking these days, UT1) is based on observations of celestial bodies averaged over the course of the year. UTC is based on atomic clocks, and is what is actually used for timekeeping mostly everywhere. It occasionally has a leap second added to keep it within 0.9 seconds of UT1, because the earth's rotation is slowing. – Michael Hampton Aug 21 '16 at 9:35

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