for National Geographic News
Most U.S. residents set their clocks one hour forward in spring and one hour back in fall. However, residents of Arizona and Hawaiialong with the U.S. territories of Puerto Rico and the Virgin Islands, among otherswill do nothing. Those locales never deviated from standard time within their particular time zones.
Contrary to popular belief, no federal rule mandates that states or territories observe daylight saving time.
Federal law simply stipulates that areas that do switch back to standard time at 2 a.m. on the last Sunday in October.
Likewise, the rule requires that regions that observe daylight saving time, or DST, begin the period at the same time on the first Sunday in April.
This is the last year, however, in which daylight saving time will fall within those days.
In 2005, the U.S. Congress passed a law extending DST by one month as of 2007. Next year, daylight saving time will begin three weeks earlier, on March 11, and end a week later, on November 4.
While the U.S. Naval Observatory in Washington, D.C., sets what is known as standard time in the country through its maintenance of atomic clocks, the observatory has nothing to do with daylight saving time.
Oversight of DST first resided with the Interstate Commerce Commission. In 1966, the U.S. Congress transferred that responsibility to the newly created Department of Transportation. Congress ordered the agency to "foster and promote widespread and uniform adoption and observance of the same standard of time within and throughout each such standard time zone."
So why is a transportation authority in charge of time laws? Bill Mosley, a public affairs officer at the U.S. Department of Transportation, explains that it all dates back to the heyday of railroads.
"In the early 19th century localities set their own time," Mosley said. "It was kind of a crazy quilt of time, time zones, and time usage. When the railroads came in, that necessitated more standardization of time so that railroad schedules could be published."
In 1883 the U.S. railroad industry established official time zones with a set standard time within each zone. Congress eventually came on board, signing the railroad time zone system into law in 1918.
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