Q: What is UT or UTC (GMT) and why do we use it? How do I convert my local time to UT?
A:
UT stands for Universal Time (also called UTC for Coordinated Universal Time).
It is widely used as a scientific reference time. GLOBE schools span many different
time zones. For example, 9:00 a.m. in Buenos Aires, Argentina is not
the same time as 9:00 a.m. in Sydney, Australia. For this reason GLOBE
schools report their measurement times in UT so that measurements from
across the world are all in a common time frame and can be compared with each other.
(UT is the time of the same zone that was previously called GMT for Greenwich Mean
Time, but it is based on atomic measurements instead of Earth's rotation.)
To convert your local time to UT, you need to know which time zone
you are in and whether or not daylight savings time (or summer time) is in effect.
(Some sources for this information are given below.)
The standard time difference between your time zone and UT is
the time difference when it is not daylight savings time. It can be found
in the table below, or from the source you used to find your time zone.
If you are west of the UT time zone (i.e. behind UT):
- The actual time difference is
the standard time difference except during daylight savings time, when one hour must be subtracted to get the actual time difference.
- UT is local time plus actual time difference.
If you are east of the UT time zone (i.e. ahead of UT):
- The actual time difference is
the standard time difference except during daylight savings time, when one hour must be added to get the
actual time difference.
- UT is local time minus actual time difference.
If you are in the UT time zone:
- Your local time is UT except during summer time (daylight savings time), when you need to subtract one hour to get UT.
You can enter your local time here to have it converted to UT, or to check your calculation:
| Local time to UT converter |
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If you are unable to determine which time zone you are in from a map, atlas, or
local source, or don't know whether or not you have daylight savings time, you may be able
to find the actual difference between your local time and UT directly. To do this, follow these
steps:
- Look up the current UT on the GLOBE website navigation bar (be sure to Refresh or Reload the page first),
or a website such as http://tycho.usno.navy.mil/utclock.html, or http://www.time.gov/timezone.cgi?UTC/s/0/java, or http://wwp.greenwichmeantime.com.
- Look up your local time.
- Find the difference between UT and your local time.
- Add, if you are behind UT, (or subtract, if you are ahead of UT), this difference to
any of your local measurement times to get the measurement times in UT.*
The following map is to help you identify which time zone you are in.
The time zones shown on the map are listed in the table below the map with their
most common names and abbreviations.
For some areas, it may be difficult to determine which zone you are in
from this map since it does not show much detail of any particular region. A larger map
which shows more detail for some areas is available at
http://www.travel.com.hk/region/timezone.htm.
(If you know your position on the time zone map, or the name of your
time zone, or the time difference from your time zone to UT, you can find the remaining
information about your time zone in the table below the map.)
| NT | Samoa Standard Time / Nome Time | 11:00 behind UT |
| HST/HAST | Hawaii-Aleutian Standard Time | 10:00 behind UT |
| HADT | Hawaii-Aleutian Daylight Time | 9:00 behind UT |
| AKST/YST | Alaska Standard Time / Yukon Standard Time | 9:00 behind UT |
| AKDT/YDT | Alaska Daylight Time / Yukon Daylight Time | 8:00 behind UT |
| PST | Pacific Standard Time | 8:00 behind UT |
| PDT | Pacific Daylight Time | 7:00 behind UT |
| MST | Mountain Standard Time | 7:00 behind UT |
| MDT | Mountain Daylight Time | 6:00 behind UT |
| CST | Central Standard Time | 6:00 behind UT |
| CDT | Central Daylight Time | 5:00 behind UT |
| EST | Eastern Standard Time | 5:00 behind UT |
| EDT | Eastern Daylight Time | 4:00 behind UT |
| AST | Atlantic Standard Time | 4:00 behind UT |
| ADT | Atlantic Daylight Time | 3:00 behind UT |
| NST | Newfoundland Standard Time | 3:30 behind UT |
| NDT | Newfoundland Daylight Time | 2:30 behind UT |
| BZT/ART | Brazil Zone 2 Standard Time / Argentina Time | 3:00 behind UT |
| BZDT | Brazil Zone 2 Daylight Time | 2:00 behind UT |
| AT | Azores Time | 2:00 behind UT |
| WAT | West Africa Time | 1:00 behind UT |
| UT/UTC/WET | (Coordinated) Universal Time / Western European Time | - |
| WEST | Western European Summer Time | 1:00 ahead of UT |
| CET/MET | Central (or Middle) European Time | 1:00 ahead of UT |
| CEST/MEST | Central (or Middle) European Summer Time | 2:00 ahead of UT |
| EET | Russia Zone 1 / Eastern European Time | 2:00 ahead of UT |
| EEST | Eastern European Summer Time | 3:00 ahead of UT |
| BT | Russia Zone 2 / Baghdad Time | 3:00 ahead of UT |
| IT/IRST | Iran Time / Iran Standard Time | 3:30 ahead of UT |
| IRDT | Iran Daylight Time | 4:30 ahead of UT |
| ZP4 | Russia Zone 3 | 4:00 ahead of UT |
| AFT | Afghanistan Time | 4:30 ahead of UT |
| ZP5 | Russia Zone 4 | 5:00 ahead of UT |
| IST | Indian Standard Time | 5:30 ahead of UT |
| NPT | Nepal Time | 5:45 ahead of UT |
| ZP6 | Russia Zone 5 | 6:00 ahead of UT |
| MMT | Myanmar Time | 6:30 ahead of UT |
| ZP7 | Russia Zone 6 | 7:00 ahead of UT |
| AWST | Russia Zone 7 / Australian Western Standard Time | 8:00 ahead of UT |
| AWDT | Australian Western Daylight Time | 9:00 ahead of UT |
| JST | Russia Zone 8 / Japan Standard Time | 9:00 ahead of UT |
| ACST | Australian Central Standard Time | 9:30 ahead of UT |
| ACDT | Australian Central Daylight Time | 10:30 ahead of UT |
| AEST | Russia Zone 9 / Australian Eastern Standard Time | 10:00 ahead of UT |
| AEDT | Australian Eastern Daylight Time | 11:00 ahead of UT |
| SBT/MAGT | Solomon Island Time / Magadan Island Time | 11:00 ahead of UT |
| NZST | New Zealand Standard Time | 12:00 ahead of UT |
| NZDT | New Zealand Daylight Time | 13:00 ahead of UT |
The above table shows the time differences during daylight savings time
below the time differences during standard time.
Since each country or state determines its own rules about whether or not,
and when, to implement daylight savings time, and these rules change, we cannot give a
fixed list of countries and times that daylight savings time is in effect. A list of most
countries that have daylight savings time can be found at http://webexhibits.org/daylightsaving/g.html. Additional time zone maps can be found at:
http://www.timeticker.com/, http://www.absolutebeginnersastronomy.com/time.html, http://wwp.greenwichmeantime.com/info/world-time-zone-map.pdf, http://www.time.gov.
*NOTES
- Most time zones differ from UT by a whole number of hours. For example,
Central European Time (CET), shown in yellow on the map, is one hour ahead of UT,
Eastern European Time (EET) is two hours ahead of UT, and so on. But there are a few
time zones, called non-standard time zones, whose time difference from UT includes a
fraction of an hour. For example, Newfoundland Standard Time is 3 hours 30 minutes behind UT.
- If you find the time difference directly, you will not need to be
concerned about whether or not it is daylight savings time, but if you change between it
being in effect and not being in effect, you will need to find the time difference again.
- Unless you are in a non-standard
time zone, this difference should be a whole number of hours. So, for example, if you get a
difference of 3 hours and 55 minutes, then the time difference is actually 4 hours and due
to time loading the page and/or inaccuracy in your local clock, an error of 5 minutes
was introduced. If you are in a non-standard time zone, the time difference will be
an exact half or quarter hour.
If you have any difficulty or questions about converting your local time to UT, please contact the Help Desk.
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