Standard Time and Daylight Saving Time

Don't forget to set your clocks back on Saturday night, November 5, or before 2:00 AM on Sunday, November 6. when daylight saving time officially ends. This is also a good weekend to replace the batteries in your smoke detectors and carbon monoxide detectors.

Daylight Saving Time (DST) is a widely used system that adjusts the local time forward from the official standard time during summer months, usually by one hour. (Please note that it is daylight saving, not savings.)

Use of daylight saving time in the United States, is governed by the Uniform Time Act of 1966. This Act provides a standard for establishing the dates when DST begins and ends in the U.S., while allowing local exemptions from its observance. Any state wishing to be exempt from DST may pass a law exempting the entire state. The states of Arizona and Hawaii do not observe DST. However, the Navajo Indian Reservation in Arizona does. In addition, American Samoa, Guam, the Northern Mariana Islands, Puerto Rico, and the U.S. Virgin Islands do not observe DST.

The Energy Policy Act of 2005 extended the start and end dates of daylight saving time in the United States. Since 2007, DST has begun on the second Sunday in March and has ended on the first Sunday in November. The U.S. Department of Energy is studying the impact of this extension of DST, and the U.S. Congress retains the right to revert to the previous schedule if the study shows it does not produce a significant savings of energy. The daylight saving time law was repealed in 1919 over a presidential veto, but reestablished nationally during World War II.

The concept of a standard time is the result of the railroads needing to know how to coordinate cross-country train schedules. Prior to 1883, local time was used throughout North America, resulting in an inordinate number of local times. On October 11, 1883, the heads of the major railroads met in Chicago to adopt the Standard Time System of four standard time zones for the continental U.S. The new system was adopted by most states almost immediately after railroads did so. The Standard Time Act of 1918 (also known as the Calder Act) established standard time everywhere within each time zone, as well as daylight saving time, as U.S. law.

The daylight saving time law was repealed in 1919 over a presidential veto, but reestablished nationally during World War II.