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 or UT 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 or 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.

Like most astronomical calculations, eclipse predictions are usually presented in terms of Universal Time. In order to convert eclipse predictions from UT to local time, you need to know what time zone you are in. For the total solar eclipse of 1998, the path of totality passes through several time zones and the coversion from UT to local time is as follows:

     Galapagos Islands:       Central Standard Time (CST)  =  UT - 6 hours
     Colombia:                Eastern Standard Time (EST)  =  UT - 5 hours
     Venezuela & Caribbean:   Atlantic Standard Time (AST) =  UT - 4 hours

This information is unofficial and is provided only as a guideline. Time zones for countries around the world can be determined with a special Time Zone Map courtesy of the HM Nautical Almanac Office, Royal Greenwich Observatory. Since time zones and local time are legislated individually by each sovereign nation, you may also want to check with a country's embassy to verify the time zone in use. Remember to also inquire about the use of daylight savings in that nation.

For other locations in the Americans, the conversion from UT to local time is as follows:

                Atlantic Standard Time (AST) =  UT - 4 hours
                Eastern Standard Time (EST)  =  UT - 5 hours
                Central Standard Time (CST)  =  UT - 6 hours
                Mountain Standard Time (MST) =  UT - 7 hours
                Pacific Standard Time (PST)  =  UT - 8 hours

For more information on time reconing and time zones, check out the following sites:

• What is Universal Time? - U.S. Naval Observatory
• Current Coordinated Universal Time - U.S. Naval Observatory
• What are the U.S. Time Zones? - U.S. Naval Observatory
• World Time Zones - R. E. Schmidt, U.S. Naval Observatory
• Systems of Time - R. E. Schmidt, U.S. Naval Observatory
• What is a Leap Second? - R. E. Schmidt, U.S. Naval Observatory
• A Walk Through Time - National Institute of Standards and Technology

WebMaster: Fred Espenak Planetary Systems Branch - Code 693 e-mail: espenak@lepvax.gsfc.nasa.gov NASA/Goddard Space Flight Center, Greenbelt, Maryland 20771 USA