The world is divided up into about 24 time zones. We say about because some states, regions or countries shift their times by half an hour from the strict 24-hour divisions. Standard time within most time zones is an integral number of hours offset from a time scale called Coordinated Universal Time (abbreviated UTC), maintained by a large number of very precise “atomic clocks” at laboratories around the world, including the U.S. Naval Observatory. UTC is a successor to Greenwich Meridian Time (GMT), although their exact definitions differ, and although GMT is no longer used within the worldwide community of scientists.
Translate UTC into your local time:
Atlantic Daylight Time| subtract 3 hours from UTC
Atlantic Standard Time| subtract 4 hours from UTC
Eastern Daylight Time| subtract 4 hours from UTC
Eastern Standard Time| subtract 5 hours from UTC
Central Daylight Time| subtract 5 hours from UTC
Central Standard Time| subtract 6 hours from UTC
Mountain Daylight Time| subtract 6 hours from UTC
Mountain Standard Time| subtract 7 hours from UTC
Pacific Daylight Time| subtract 7 hours from UTC
Pacific Standard Time| subtract 8 hours from UTC
Alaska Daylight Time| subtract 8 hours from UTC
Alaska Standard Time| subtract 9 hours from UTC
Hawaii-Aleutian Standard Time| subtract 10 hours from UTC
Samoa Standard Time| subtract 11 hours from UTC
Greenwich Mean Time| same as UTC
British Summer Time| add 1 hour to UTC
Central European Time| add 1 hour to UTC
Central European Summer Time| add 2 hours to UTC
Eastern European Time| add 2 hours to UTC
Eastern European Summer Time| add 3 hours to UTC
Charlie Time (Mid East)| add 3 hours to UTC
Delta Time (Mid East)| add 4 hours to UTC
Western Standard Time| add 8 hours to UTC
Western Summer Time| add 9 hours to UTC
Central Standard Time| add 9:30 hours to UTC
Central Summer Time| add 10:30 hours to UTC
Eastern Time| add 10 hours to UTC
Eastern Summer Time| add 11 hours to UTC
Examples of how to convert from UTC to your local time
Let’s say you live in Houston, Texas, which is in Central Standard Time (U.S.). To convert 18 UTC into your local time, subtract 6 hours, to get 12 CST. During daylight saving (summer) time, you would only subtract 5 hours, so 18 UTC would convert to 13 CDT.
Or, let’s say you’re in Paris, France, which is in Central European Time. To convert 18 UTC into your local time, add 1 hour, to get 19 CET. In summer, add 2 hours to get 20 CEST.
When converting zone time to or from UTC, dates must be properly taken into account. For example, 10 March at 02 UTC is the same as 9 March at 21 EST (U.S.).
The table can also be used to determine the difference between the time observed in any two zones. For example, the table shows that Eastern Standard Time is three hours ahead of Pacific Standard Time (U.S.).
Bottom line: The Earth has 24 time zones, but when astronomers mention a time, it’s often Coordinated Universal Time, or UTC. This article explains how to translate UTC to your local time zone.