Cooridinated Universal Standard Time

Most of the United States begins Daylight Saving Time at 2:00 a.m. on the second Sunday in March and reverts to standard time on the first Sunday in November. Parts of Arizona and Hawaii do not use Daylight Saving time.

*During the eight-month period of Daylight Saving Time, the names of time in each of the time zones in the U.S. change as well.

Eastern Standard Time (EST) becomes Eastern Daylight Time (EDT)

Central Standard Time (CST) becomes Central Daylight Time (CDT)

Mountain Standard Time (MST) becomes Mountain Daylight Time (MDT)

Pacific Standard Time becomes Pacific Daylight Time (PDT)

History of Daylight Saving Time

Daylight Saving Time was instituted in the United States during World War I in order to save energy for war production by taking advantage of the later hours of daylight between April and October. During World War II the federal government again required the states to observe the time change. Between the wars and after World War II, states and communities chose whether or not to observe Daylight Saving Time. In 1966, Congress passed the Uniform Time Act, which standardized the length of Daylight Saving Time.

Daylight Saving Time is four weeks longer since 2007 due to the passage of the Energy Policy Act in 2005. The Act extended Daylight Saving Time by four weeks from the second Sunday of March to the first Sunday of November, with the hope that it would save 10,000 barrels of oil each day through reduced use of power by businesses during daylight hours. Unfortunately, it is exceedingly difficult to determine energy savings from Daylight Saving Time and based on a variety of factors, it is possible that little or no energy is saved by Daylight Saving Time.

*About.com/Geography