Time Zones Key
Fred Espenak
Introduction
Time can be measured in a number of ways. For instance, we can measure the passage of time via the orbital motion of Earth and other planets in the solar system (Dynamical Time). Or we can measure time based on the rotation of Earth on its axis with respect to the stars (Universal Time). Finally, we can measure time through the oscillations of atoms (International Atomic Time).
Universal Time (UT1) is the precise measure of time used as the basis for all civil time-keeping. Although their exact definitions differ, most readers can assume that Universal Time is equivalent to Greenwich Mean Time (GMT). Universal Time is actually based on the mean sidereal time as measured in Greenwich, England. It's also approximately equal to mean solar time from Greenwich.
Most astronomical predictions are usually presented in terms of Universal Time. The Universal Time (UT1) can be converted to local time when applying the appropriate offset.
The Time Zone drop down menu permits the choice of one of twenty-four time zones around the world. The available time zones, the offsets from Universal Time (UT1), the primary time zone name, and the general geographic region is listed in the following table. Note that most time zones have multiple names based on the countries they pass through. The table below includes a single name for each time zone.
| Time Zones Key | |||
| Time Zone Label | UT1 Offset | Time Zone(s) | Regions |
| UT1/GMT/London | 0 hr | GMT (Greenwich Mean Time) | U.K. |
| UT1+1/CET/Europe | + 1 hr | CET (Central European Time) | Central Europe |
| UT1+2/EET/E.Europe | + 2 hr | EET (Eastern European Time) | Eastern European |
| UT1+3/MSK/Moscow | + 3 hr | MSK (Moscow Standard Time) | Moscow |
| UT1+4/GST/Gulf | + 4 hr | GST (Gulf Standard Time) | Persian Gulf |
| UT1+5/PKT/Pakistan | + 5 hr | PKT (Pakistan Standard Time) | Pakistan |
| UT1+6/BST/Bang. | + 6 hr | BST (Bangladesh Standard Time) | Bangladesh |
| UT1+7/WIB/Java | + 7 hr | WIB (Western Indonesian Time) | W. Indonesia |
| UT1+8/CST/China | + 8 hr | CST (China Standard Time) | China |
| UT1+9/JST/Japan | + 9 hr | JST (Japan Standard Time) | Japan |
| UT1+10/AEST | + 10 hr | AEST (Australia Eastern Time) | E. Australia, Guam |
| UT1+11/NCT | + 11 hr | NCT (New Caledonia Time) | New Caledonia |
| UT1+12/NZST | + 12 hr | NZST (New Zealand Time) | New Zealand |
| UT1-11/SST/Somoa | - 11 hr | SST (Somoa Standard Time) | Somoa |
| UT1-10/HAST/Hawaii | - 10 hr | HAST (Hawaii-Aleutian Standard Time) | Hawaii, Aleutians |
| UT1-9/AKST/Alaska | - 9 hr | AKST (Alaska Standard Time) | Alaska |
| UT1-8/PST | - 8 hr | PST (Pacific Standard Time) | western USA < Canada |
| UT1-7/MST/PDT | - 7 hr | MST (Mountain Standard Time) PST (Pacific Daylight Time) | western USA < Canada |
| UT1-6/CST/MDT | - 6 hr | CST (Central Standard Time) MDT (Mountain Daylight Time) | western/central USA < Canada |
| UT1-5/EST/CDT | - 5 hr | EST (Eastern Standard Time) CDT (Central Daylight Time) | central/eastern USA < Canada |
| UT1-4/AST/EDT | - 4 hr | AST (Atlantic Standard Time) EDT (Eastern Daylight Time) | eastern USA < Canada |
| UT1-3/WGT | - 3 hr | WGT (Western Greenland Time) | W. Greenland |
| UT1-2/EGT | - 2 hr | EGT (Eastern Greenland Time) | E. Greenland |
| UT1-1/AZOT | - 1 hr | AZOT (Azores Standard Time) | Azores |
If Daylight Saving Time is in effect in the time zone, then one hour must be ADDED to the standard time.
For example, let's assume that an eclipse begins in Toledo, Ohio on June 20 at 20:25 UT1. Toledo is in the Eastern Standard Time zone, so:
Local Time = 20:25 - 5 hours
= 15:25 (= 3:25 pm)
But since Toledo observes Daylight Saving Time in June, we must ADD one more hour to the standard time. So the local time in Toledo is 16:25 (=4:25pm).
World Time Zones
World Time Zones (click to see larger image)
Time zones for countries around the world can be determined using the map above. You also need to know if Daylight Saving Time is practiced during that time of year.
Coordinated Universal Time
Coordinated Universal Time (UTC) is based on atomic time. It is synchronized and adjusted to stay within 0.9 seconds of Universal Time (UT). Occasionally, a "leap second" is added to UTC in order keep it in sync with UT (which varies due to Earth's rotation). UTC is the time used by GPSs and is the standard reference for Time Zones around the world.
The official source of time used in the United States is the Time Service Department of the U.S. Naval Observatory. The current UTC is shown below:
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U.S. Naval Observatory Master
Clock
Reload Frame to Update Clock
You can use the time on the U.S.N.O. Master Clock to determine how many hours different your local time is from Universal Time. Once noted, use this number to convert all eclipse prediction times from UT to your own local time.
For example, if you are in the Eastern Standard Time zone, you will see that your local time is 5 hours earlier than UT. In order to convert any eclipse predictions from UT to local time (i.e. - EST), you must subtract 5 hours from UT:
Local Time = UT - 5 hours
Time Zone Links
For more information on time reckoning and time zones, check out the following sites:
- A Walk Through Time - National Institute of Standards and Technology
- Systems of Time - R. E. Schmidt, U.S. Naval Observatory
- What is a Leap Second? - R. E. Schmidt, U.S. Naval Observatory
- Precise Time - Naval Oceanography Portal
- Time Zones - Wikipedia
- U.S. Time Zone - Wikipedia
- Local Times Around the World - dateandtime.com
- World Time Zones - worldtimezone.com