As I visit schools, I have found that some students have a surprising misconception. They think Daylight Saving Time results in more daylight hours. I suppose this comes about as they notice that sunset occurs an hour later. But Daylight Saving Time shifts both sunrise and sunset times. So, we experience the same amount of daylight before and after Daylight Saving Time.

Well, almost . . .

A close look at sunrise and sunset times for Salt Lake City on March 13 and 14, 2010 reveals that March 14 has 2 minutes more daylight than March 13.

Saturday, March 13, 2010         Mountain Standard Time
Sunrise                    6:42 a.m.
Sunset                     6:32 p.m.
Sunday, March 14, 2010         Mountain Daylight Time
Sunrise                    7:41 a.m.
Sunset                     7:33 p.m.

This is NOT the result of Daylight Saving Time. Instead, it comes about as Earth orbits the Sun. Earth rotates on its axis once a day. Earth also orbits, or revolves around the Sun once each year. Earth’s rotational axis is tilted by about 23.4º and points in a nearly constant direction as Earth circles the Sun. This is evidenced by the northern axis pointing toward Polaris, the North Star.

Diagram of Earth's orbit around the Sun.

While the axis continues to point in the same direction, it’s orientation to the Sun changes. Back on December 21, Earth was at the place in its orbit where the northern axis leans most away from the Sun. On this day, Salt Lake City experiences about 9 hours of daylight. As Earth continues to move around the Sun, the angle between the axis and the Sun decreases. This results in an increase in the hours of daylight. This continues until June 21, when Earth reaches the place in its orbit where the northern axis leans most toward the Sun. On that day, Salt Lake City will experience about 15 hours of daylight.

Earth will continue in its orbit and eventually Daylight Saving Time will end with a 25 hour day on November 7, 2010.

Seems a common sentiment, although not scientifically accurate.

Sunday, November 1st, 2009, marks the end of Daylight Saving Time (note: It is Daylight Saving Time, not Daylight Savings Time), where we need to move our clocks back one hour, preferably before retiring Saturday night. Thus, we get an extra hour’s sleep Sunday morning. Officially, in the United States, we are supposed to set our clocks back at 2:00 a.m. to 1:00 a.m., thus living one hour over again.

Nobody gains or loses hours because of Daylight Saving Time. We adjust our clocks simply to move one hour of early morning sunlight to the evening part of the day each spring (DST begins the 2nd Sunday in March), presumably because more people want to do outdoor things at 7 p.m. rather than 7 a.m.

Used to be (prior to 2008) that we changed our clocks forward on the 1st Sunday in April, and back on the last Sunday in October. However, in 2007 a law was passed to officially add one month to the DST period, by pushing up the ’spring forward’ date by three weeks and the ‘fall back’ date by one week.

This works well for Halloween. Parents taking their little one’s out at 6 p.m. under old system were walking in the dark, because DST ended, always, the Sunday before Halloween. Now, DST ends, always, the Sunday after Halloween, so it is still light outside at 6 p.m. Older kids still wait until it’s dark outside anyway…

Daylight Saving Time is not a universal standard. Even within the US, Hawaii and Arizona, along with Guam, Puerto Rico and other US territories, do not follow DST at all. The European Union still follows a DST calendar from April to October. Most nations in the tropical zone do not follow DST because their sunrise/sunset times do not vary much throughout the year. Only a few countries on the African continent follow DST at all.

Is it still a good idea? It depends on who you ask. Yes, it saves energy because you don’t have to turn on your lights at home so early in the evening. Golfers can knock off work a little early and still get in a round while the sun is up. Home gardeners get that extra hour of daylight in the evening to weed the tomatoes.

Me, personally…I, just once, want to fly from St. George, Utah to Flagstaff, Arizona on some summer day. I believe it’s about a half hour flight. That way I can arrive…before I left.