for National Geographic News
Daylight saving time in most of the United States ends this Sunday, November 2, at 2 a.m. local time—only the second year it's ending in November. Since its passage into law in 1918, the system has seen many changes, most recently with a supposedly energy-saving extension signed into law into in 2005.
(See "Daylight Saving Change: Energy Boon or Waste of Time?" [March 9, 2007].)
Contrary to popular belief, no federal rule mandates that states or territories observe daylight saving time.
Most U.S. residents set their clocks one hour forward in spring and one hour back in fall. But residents of Hawaii and most of Arizonaalong with the U.S. territories of Puerto Rico and the Virgin Islands, among otherswill do nothing. Those locales never deviate from standard time within their particular time zones.
Federal law simply stipulates areas that observe daylight saving time must switch back to standard time at 2 a.m. on the first Sunday in November.
Likewise, the rule requires that regions that observe daylight saving time begin the period at the same time on the second Sunday in March.
The Dawn of Daylight Saving Time
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 daylight saving time 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 transportation 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? It all dates back to the heyday of railroads.
"In the early 19th century localities set their own time," said Bill Mosley, a public affairs officer at the U.S. Department of Transportation.
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