Coordinated Universal Time (UTC)

Greenwich Mean Time (GMT) became a time standard in the 19th century for British maritime navigation.   Greenwich, England was established as the "Prime Meridian" (longitude = 0 degrees) and the Royal Observatory was built at Greenwich. In 1970 the Coordinated Universal Time (UTC) system was devised by an international advisory group of technical experts within the International Telecommunication Union (ITU). Based on GMT, but to be a worldwide standard, the ITU felt it was best to designate a single abbreviation for use in all languages. As a compromise, UTC was chosen.  

UTC (or GMT) is now a standard used throughout the world. All time zones are computed relative to UTC. For example, in the United States, Central Standard Time (CST) is 6 hours earlier than UTC time -- 10:00 UTC is 4:00 CST.

You can use the chart below to find your time relative to UTC. Here is how:

1. Locate where you are on the world map.
2. Match the color with the number directly below your location.
3. If it is day-light savings right now where you live, you must add one hour to this number.

The calculated number is the number of hours from UTC that your local clocks should display.

In addition to the various other clocks we use at NASA, we use UTC clocks for things that must happen at fixed calendar times. Though most of a mission might run using an MET clock, a new conference would be scheduled in UTC for the convenience of the reporters.

There are UTC clocks on board the shuttle; the other on-board clock is the MET clock.

Other "clocks"

| MET | GMT | Countdown & Liftoff | Flight day | Apollo era |