The United States. Daylight saving time, also called “summer time,” is the practice of advancing clocks forward by one hour in the spring to gain additional daylight during the early evening. In the fall, clocks are again turned back an hour. The U.S. federal law that established “daylight time” in this country does not require its observance. Arizona, Hawaii, and the territories of Puerto Rico, Virgin Islands, and American Samoa do not use DST. These areas receive so much sun throughout the year that gaining another hour of sunlight in the summertime is not seen as a benefit.

DST Dawns in Indiana. Until April 2005, when Indiana passed a law agreeing to observe daylight saving time, the Hoosier state had its own unique and complex time system. Not only is the state split between two time zones, but until recently, only some parts of the state observed daylight saving time while the majority did not. Under the old system, 77 of the state's 92 counties were in the Eastern time zone but did not change to daylight time in April. Instead they remained on standard time all year. That is, except for two counties near Cincinnati, Ohio, and Louisville, Ky., which did use daylight time. But the counties in the northwest corner of the state (near Chicago) and the southwestern tip (near Evansville), which are in the central time zone, used both standard and daylight time.

The battle between the old system and DST was contentious and hard-won. Bills proposing DST had failed more than two dozen times before it squeaked through the state legislature in April 2005. In April 2006, Indiana joined 47 other states in observing DST for the first time.

Around the World. About 70 countries around the world observe daylight saving time in some form. Here are some interesting facts:

• Most of Canada uses DST. Some exceptions include the majority of Saskatchewan and parts of northeastern British Columbia. In the fall of 2005, Manitoba and Ontario announced that like the United States, they would extend daylight time starting in 2007. The attorney general of Ontario commented that “it is important to maintain Ontario's competitive advantage by coordinating time changes with our major trading partner, and harmonizing our financial, industrial, transportation, and communications links.” Most other provinces have indicated that they will follow suit.
• It wasn't until 1996 that Mexico adopted DST. Now all three Mexican time zones are on the same schedule as the United States.
• Also in 1996, members of the European Union agreed to observe a “summertime period” from the last Sunday in March to the last Sunday in October.
• Most countries near the equator don't deviate from standard time.
• In the Southern Hemisphere, where summer arrives in what we in the Northern Hemisphere consider the winter months, DST is observed from late October to late March.
• Three large regions in Australia do not participate in DST. Western Australia, the Northern Territory, and Queensland stay on standard time all year. The remaining south-central and southeastern sections of the continent (which is where Sydney and Melbourne are found) make the switch. This results in both vertical and horizontal time zones Down Under during the summer months.
• China, which spans five time zones, uses only one. The entire country is always eight hours ahead of Universal Time and it does not observe DST.
• In Japan, DST was implemented after World War II by the U.S. occupation. In 1952 it was abandoned because of strong opposition by Japanese farmers.

U.S. Daylight Saving Time Schedule

The year 2006 will be the last year in which clocks are set forward one hour on the first Sunday in April at 2:00 a.m. local time and set back one hour the last Sunday in October, also at 2:00 a.m. Starting in 2007, DST will be observed from the second Sunday in March to the first Sunday in November, adding a month to daylight saving time.