Standard Time Around the World

  1. Greenwich Mean Time and the Prime Meridian
  2. Time Zones: International
  3. Time Zones: United States
  4. International Time Adjustments
  5. International Date Line

Standard time was fixed in 1883 to prevent the myriad of short time differences that would result if every locality determined the mean solar time by different meridians, depending on the longitude of the particular place. Lines at every 15° longitude were drawn down a map of Earth to create 24 international time zones differing from each preceding and following zone by one hour. Because of political boundaries, such lines often depart from the strict 15° rule and sometimes zigzag or demarcate ares that differ by half an hour only.

The continental United States has four meridians designated to determine standard times: 75° , 90° , 105° , and 120° west of Greenwich, England. Alaska Standard Time is determined by the meridian at 135° west of Greenwich and Hawaii-Aleutian Standard Time is set at the 150° meridian.

Canada has a total of six time zones: the four that apply in the continental United States and an additional two in the east. Atlantic Standard Time is based on 60° west of Greenwich and is one hour ahead of Eastern Standard Timel Newfoundland Standard Time, based on 52° 30' west, is 30 minutes ahead of Atlantic Standard Time.

Puerto Rico is in the Atlantic Standard Time zone.

Greenwich Mean Time and the Prime Meridian

The mean solar time determined by the meridian that runs through Greenwich, England (Greenwich Mean Time), is called Universal Time. It is used all over the world in navigation, both air and sea, and for scientific purposes, as in astronomy. From Greenwich, too, longitudes are measured around the world, Greenwich being 0° , called the prime meridian.

Time Zones: International

The following table gives the time in cities around the world when it is 12 noon Eastern Standard Time. An asterisk indicates the morning of the following day.
Addis Ababa 8 PM Alexandria 7 PM Amsterdam 6 PM Athens 7 PM
Baghdad 8 PM Bangkok 12 M Barcelona 5 PM Beijing 1 AM
Belfast 5 PM Belgrade 6 PM Berlin 6 PM Bogotá 12 N
Bombay 10:30 PM Brasília 2 PM Brussels 6 PM Bucharest 7 PM
Budapest 6 PM Buenos Aires 2 PM Cairo 7 PM Calcutta 10:30 PM
Calgary 10 AM Cape Town 7 PM Caracas 1 PM Casablanca 5 PM
Copenhagen 6 PM Delhi 10:30 PM Dublin 5 PM Edinburgh 5 PM
Florence 6 PM Frankfurt 6 PM Geneva 6 PM Glasgow 5 PM
Halifax 1 PM Hanoi 1 AM* Havana 12 N Helsinki 7 PM
Ho Chi Minh City 1 AM* Hong Kong 1 AM* Istanbul 7 PM Jakarta 12 M
Jerusalem 7 PM Johannesburg 7 P.M. Karachi 10 PM Kuala Lumpur 1 AM*
Lima 12 N Lisbon 5 PM Liverpool 4 PM Madridh 5 PM
Managua 11 AM Manila 1 AM* Marseilles 6 PM Mecca 8 PM
Melbourne 4 AM* Mexico City 11 AM Montreal 12 N Moscow 8 PM
Munich 6 PM Naples 6 PM Oslo 6 PM Ottowa 12 N
Panama 12 N Paris 6 PM Prague 6 PM Quebec 12 N
Rio de Janeiro 2 PM Riyadh 8 PM Rome 6 PM St. Petersburg 8 PM
San Juan 1 PM Santiago 1 PM Seoul 2 AM* Shanghai 1 AM*
Stockholm 6 PM Sydney 4 AM* Tangiers 5 PM Teheran 8:30 PM
Tel Aviv 7 PM Tokyo 2 AM Toronto 12 N Tripoli 7 PM
Vancouver 9 AM Venice 6 PM Vienna 6 PM Vladivostok 3 AM*
Warsaw 6 PM Winnipeg 11 AM Yangon 11:30 PM Yokohama 2 AM*
Zurich 6 PM

Time Zones:United States

The "lower 48" U.S. states and Washington, D.C. are divided into 4 time zones: Eastern, Central, Mountain, and Pacific. The time in each zone is one hour earlier than in the zone to its east and one hour later than in the zone to its west. The basic pattern of time zones in states is given below. An asterisk indicates the state falls into two time zones.
Eastern, 12N Central, 11 A.M. Mountain, 10 A.M. Pacific, 9 A.M.
Connecticut Alabama Arizona California
Delaware Arkansas Colorado Idaho*
District of Columbia Florida* Idaho* Nevada
Florida* Illinois Kansas* Oregon*
Georgia Indiana* Montana Washington
Indiana* Iowa Nebraska*
Kentucky* Kansas* New Mexico
Maine Kentucky* North Dakota*
Maryland Louisiana Oregon*
Massachusetts Michigan* South Dakota*
Michigan* Minnesota Texas*
New Hampshire Mississippi Utah
New Jersey Missouri Wyoming
New York Nebraska*
North Carolina North Dakota*
Ohio Oklahoma
Pennsylvania South Dakota*
Rhode Island Tennessee*
South Carolina Texas*
Tennessee* Wisconsin
Vermont
Virginia
West Virginia