Where the techniques of Maths
are explained in simple terms.
UTC time Vs Local time.
- Algebra & Number
- Calculus
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- Maths & beyond
- Index
Current UTC time.
We can refer to time in any location in two ways:
- as the local time;
This is simply the time at the place you are right now. You may or may not be on a special Daylight Saving time depending on the time of the year.
- as Universal Time Coordinated (UTC) or Coordinated Universal Time:
This name is the primary standard for time and from this standard, all other clocks in the world are set relative to that standard.
The UTC time is never adjusted for Daylight Saving. The basic reference point for UTC is the Royal Observatory in Greenwich, England. So all times are either before that time or after - and are indicated with + or -.
Wikipedia describes why the initials do not reflect the order of the words.
Coordinated Universal Time was first adopted - albeit informally - on 1 January 1960. The official abbreviation of UTC and the official English name of Coordinated Universal Time (along with the French equivalent) were not however adopted until 1967.
UTC is now used around the world for many tasks - for example to synchronise the clock on your computer and on all other computers ... and for other activities including
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| to help coordinate all weather forecasts (including for example) the path of Cyclone Yasi over Australia). |
for activities on and for the International Space Station; | to establish flight paths for traffic control in aviation (like those shown here in a 3 hour period over England). |
The basic time and the Prime Meridian.
All times throughout the world are based on locations relative to Greenwich. The term the PRIME MEREDIAN describes the longitude passing through Greenwich.
- times at locations east of Greenwich are indicated by a + (for example UTC+10 meaning 10 hours ahead of Greenwich);
- times at locations west of Greenwich are indicated by a - (for example UTC-4 meaning 4 hours behind Greenwich);.
For example, if it were 10:00 am in Greenwich:
- a location with UTC +10 would have a local time of 8:00 pm (so 10 hours ahead of the time at Greenwich);
- a location with UTC -4 would have a local time of 6:00 am (so 4 hours behind the time at Greenwich).
Greenwich Mean Time (GMT) is the reference used officially prior to 1972. UTC has replaced it. The critical difference between UTC and GMT is that:
- GMT is a time zone; while
- UTC is a time standard.
The International date line.
As there are 24 hours in a day, the furthest we can measure to the east is UTC+12 and the furthest we can measure to the west is UTC-12.
Naturally these two times are both half way around the world from Greenwich - so geographically on the opposite side of Earth from Greenwich. They are really at the same place but you approach that place from opposite sides. We refer to the longitude at that place as the International Date line (IDL).
Great and small circles.
Circles can be drawn either horizontally or vertically around Earth.
To convert the UTC time given at the top of this page into times in Australia, if you are in:
Eastern Summer Time |
add 11 hours. add 10 hours. add 10:30 hours. add 9:30 hours. add 9 hours. add 8 hours. |
For other time zones throughout the world, visit the World Time Zone site.