The phrase is ´spring ahead, fall back´, and it reminds us which way to turn our clocks each spring and fall for Daylight Savings Time. Why do we change our clocks, and when do we do it?

The US changes its clocks on the first Sunday of April and the last Sunday of October. Each time zone does it at 2am. The European Union does it the last Sunday of March and the last Sunday of October, with the entire union doing it at 1am GST.

The Idea of Time
Sundials have been around for thousands of years, but those vary from location to location. The idea of a ´centralized time´ started in the middle ages, with mechanical clocks. Even these were set so that noon was when the sun was directly overhead. It wasn´t until trains began running in England in the early 1800s that ´centralized time´ really mattered. However, with trains, timetables became important, and by the late 1800s, almost all countries used some form of standardized time.

Why Alter the Clocks?
The main reason is to be most active during daylight hours, and to save electricity. Most countries see up to 5% energy savings by altering the clocks so that most people are doing things when there is natural light. Not only is there less need for light while people are home, but people also stay outdoors longer in the evening because there is light to do things. Because they are not home using electricity, the savings are even greater.

The US experimented with extra DST during the energy crisis of the early 70s, and found that the extra time did save 10,000 barrels of oil worth of energy a day. It also reduced traffic accidents, because people were driving more in the light where they could see, and reduced crime, because people were doing things in the light instead of in the dark.

Who Came Up with This?
The idea of altering clocks to make better use of sunlight was first proposed by Ben Franklin, and was taken up by London builder William Willett. He brought a bill into the House of Commons several times, but was laughed at. When Germany began using this time change to save energy in WW1, England followed suit, with the first day being May 21, 1916. The US joined in on March 19, 1918.

The changes were at first confusing in each nation that they affected, but eventually the system became understood. In fact, during WW2 England had ´Double Summer Time´ to even further increase its energy savings. Russia keeps itself one hour ahead in general, to save energy, and in the summer it moves two hours ahead to take advantage of the extra light.

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