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Coordinated Universal Time

Local time is based on time zone and Coordinated Universal Time (UTC). UTC is commonly referred to as International Time, Universal Time (UT), Zulu Time (U.S. military), or Greenwich Mean Time (GMT). GMT was established by international conference in 1884 as International Time.

The earth is divided into 24 time zones, -11 to +12. Each time zone is 1 hour long, or 15° wide in longitude. Greenwich England is, by definition, in the middle of Time Zone 0, the prime meridian. UTC time is the local time at Greenwich England. Time in other locations will be the UTC time hour plus or minus the local Time Zone. Daylight savings time adds 1 hour to the local standard (real) time.

Twenty four hour time does not use "am" or "pm", but courts hours from midnight (0 hours) to 11 pm (23 hours).

AM / PM and 24 Hour Time
12 1 2 3 4 5 6 7 8 9 10 11 am
0 01 02 03 04 05 06 07 08 09 10 11 hours
12 1 2 3 4 5 6 7 8 9 10 11 pm
12 13 14 15 16 17 18 19 20 21 22 23 hours


UNIVERSAL TIME

Time Around the World
Time zone & local time (Standard)
-11 -10 -9 PST
-8
MST
-7
CST
-6
EST
-5
-4 -3 -2 -1 UT
0
+1 +2 +3 +4 +5 +6 +7 +8 +9 +10 +11 +12

UTC Zones
Hours behind (-), or ahead of, UT
EST - Eastern Standard Time
CST - Central Standard Time
MST - Mountain Standard Time
PST - Pacific Standard Time
Chart Time Zone Chart (PDF file)
8.5 x 14 inches, 240 kB, color

Daylight savings time (DST) is used in the summer months in some regions. DST is 1 hour ahead of standard time. There is no consistency between regions as to when DST takes affect, or reverts back to standard (real) time. DST was never practical and will eventually be phased out (obsolete).

Zone -8
PACIFIC TIME (PT)
San Francisco
Zone -7
UTC -7
Phoenix
MOUNTAIN TIME (MT)
Denver, Gallup
Zone -6
CENTRAL TIME (CT)
Houston, Chicago
Zone -5
EASTERN TIME (ET)
New York, Miami
Zone -4
UTC -4

Zone -3
Rio De Janeiro,
Sao Paulo
St Pierre,
Greenland

Zone 0
UT Dublin
London
Zone +1
Berlin, Rome,
Paris, Prague
Zone +2
Beirut Cairo Jerusalem Athens, Helsinki,
Istanbul, Minsk
Zone +3

Moscow

Baghdad
Zone +4

Dubai

Zone +7

Jakarta
Zone +8
Hong Kong,
Beijing
Zone +9
Seoul,
Tokyo
Zone +10
Melbourne,
Sydney
Brisbane Vladivostok
Zone +12

Kamchatka
----
Zone -10
HAWAII–
ALEUTIAN
Zone -9
ALASKA
Anchorage


DEFINITIONS REFERENCE: A Briefer History of Time -- Howard Barnes, Georgi Dobrovolski Solar Observatory, New Zealand, 2010. (PDF version)

Standard Date Format
Virtually the entire world formats time as Hours:Minutes:Seconds (hours listed before minutes, minutes listed before seconds). The date format Year-Month-Day has become widely accepted as a standard in many countries.

Year Month Day

International Standard ISO 8601,
United States ANSI X3.30 and NIST FIPS 4-1,
Canadian standard CSA Z234.5,
European standard EN 28601,
British standard BS EN 28601.


Year 2000
The United States and many other countries use the Christian Gregorian calendar to mark years. This calendar has become a standard in such worldwide industries as aviation, and international commerce and trade -- however, other calendars do exist.

       CALENDAR    YEAR

         Jewish    5760-5761
        Chinese    4698 (Year of the Dragon)
      Old Roman    2753
       Buddhist    2544
      Christian    2000
         Coptic    1716
        Islamic    1420-1421

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Coordinated Universal Time
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