A Return to Standard Time

As if we didn't have enough to do.

This Sunday marks the end of Daylight Savings Time and a return to Standard Time. Standard tiime generally begins each year at 2 a.m. on the first Sunday of November. American's move thier clocks back one hour to return to Standard Time. Daylight Saving time and Time zones are regulated by the U.S. Department of Transportation, not by NIST.

In 2008, Daylight Saving Time begins on March 9 and ends on Nov.2.

In 2009, Daylight Saving Time begins on March 8 and ends on Nov.1.

Standard time in time zones was instituted in the U.S. and Canada by the railroads on November 18, 1883. Prior to that, time of day was a local matter, and most cities and towns used some form of local solar time, maintained by a well-known clock (on a church steeple, for example, or in a jeweler's window). The new standard time system was not immediately embraced by all, however. (The train at right is a Union locomotive used during the American Civil War, photo ca. 1861-1865.)

The use of standard time increased because of its practical advantages for communication and travel. Standard time in time zones was established by U.S. law with the Standard Time Act of 1918, enacted on March 19. Congress adopted standard time zones based on those set up by the railroads, and gave the responsibility to make any changes in the time zones to the Interstate Commerce Commission, the only federal transportation regulatory agency at the time. When Congress created the Department of Transportation in 1966, it transferred the responsibility for the time laws to the new department.

Time zone boundaries have changed greatly since their original introduction and changes still occasionally occur. The Department of Transportation conducts rulemakings to consider requests for changes. Generally, time zone boundaries have tended to shift westward. Places on the eastern edge of a time zone can effectively move sunset an hour later (by the clock) by shifting to the time zone immediately to their east. If they do so, the boundary of that zone is locally shifted to the west; the accumulation of such changes results in the long-term westward trend. The process is not inexorable, however, since the late sunrises experienced by such places during the winter may be regarded as too undesirable. Furthermore, under the law, the principal standard for deciding on a time zone change is the "convenience of commerce." Proposed time zone changes have been both approved and rejected based on this criterion, although most such proposals have been accepted.

NIST's Time and Frequency Division, FAQs page

	You can download software from NIST and USNO in order to use the Internet to automatically set your computer clock to the correct time.
	For a more detailed time zone map, look at our map of US time zones.
	For time zone offsets around the world, please consult our world time zone map.