Greenwich Mean Time and World Time Zones Local Time in Different Locales It's easy to know what time it is in your classroom right now -- just look at the clock. But do you know what time it is in another classroom across the world? How can you figure this out? Map of World Time Zones Click Map to see all 24 time zones Calculating Local Time Using World Time Zones One way is to use world time zones to count how many hours different a location is from you. The twenty-four time zones correspond to meridians of longitude. Specifically, the zones are spaced 15 degrees apart, and each time zone differs from its adjacent time zone by one hour (earlier or later). That way, the times in each zone align with the local solar times of sunrise and sunset. But using the time zones can be confusing for several reasons. First, some countries have several different time zones, and those local zones don't always align perfectly with specific longitude lines. Also, remember that with 24 time zones the local time at another location can be anywhere from 0 to 24 hours different from you, and it can even be a different date! Calculating Local Time Using Greenwich Mean Time What if you could somehow use just one single uniform time zone all around the world, would that make it easier to know what the time is at another location? That's exactly what Greenwich Mean Time or "GMT" was designed to do--to provide a single time keeping method, a single time zone, that everyone would understand, and which would avoid the confusion of local time zones. That's why it is also called Universal Time (UT). What is GMT Based On? GMT is based on the local time in Greenwich, England. That means that GMT time keeping is the same time as it is in Greenwich England. Because GMT is based on this single time zone, it is a uniform standard time keeping method. Therefore, if you are using GMT to designate a specific time, your own local time no longer matters. Check the Greenwich Mean Time Clock What is GMT Used For? Because GMT is an international time keeping standard, it is used in important applications such as official international matters, railroads, other mass transit, in military time keeping, and also in scientific applications such as satellites, weather, or astronomy. In addition, GMT was used long ago in sea navigation, in order for sailors to estimate their approximate longitude coordinate. Try This! Plan an International Call Using GMT and Time Zones >> This Season Teachers Kids Orientation Registration Search Copyright 1997-2008 Journey North. All Rights Reserved. Questions or comments? Contact us.