Saturday, March 8, 2008

Daylight Saving Time

Tonight at 2:00 AM, the United States will change its clocks forward one hour for Daylight Saving Time (DST). The US has extended DST so that it now lasts from the second Sunday in March through the first Sunday in November. To keep it official, clocks should be changed at exactly 2:00 AM.

Benjamin Franklin was one of the first to suggest changing the time in this fashion. He wrote an essay on the subject in 1784 called "An Economical Project". He was living in Paris at the time and noticed that many Parisians slept quite late into the day, but then burned candles while staying up late at night. This resulted in thousands of pounds of candles burned needlessly: if they'd change the time on their clocks they could still keep the same hours but "save" the daylight for the times when they were awake.
Europeans also have their own version of DST: it's called SummerTime, and it begins on the last Sunday in March, at 1 AM Greenwich Mean Time.

If you live near the equator, day and night keep nearly the same length for the entire day. For this reason, people living in the Tropics do not usually adjust their clocks in this way. In the temperate zones, however, the length of night and day change throughout the year.
Everyone notices that the days get longer during the spring and summer. This happens both ways: the sun stays up later at night, and it also comes up earlier in the morning. Extended daylight in the evening is terrific, but there aren't too many people who'd be happy if the sun rose at 3:30 AM.

These excessively early-morning sunrises are mitigated by DST, and in exchange we can enjoy sunlight until late evening during high summer.

There are numerous other benefits to DST. There are fewer traffic accidents, because it's brighter during the early evening when most people drive home. There are fewer violent crimes, because there are fewer such crimes committed during daylight. Many people even believe it saves energy: that we're awake fewer hours during darkness and therefore use less electricity for lighting.
By extending DST into November, it even makes it safer for Trick-or-treaters on Halloween.

There are some interesting articles on DST, along with the exact, official US time for your time zone at time.gov. Accurate to within 0.3 seconds.

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