Everything you've ever wanted to know about Daylight Savings Time

Curious? about why we change our clocks for back an hour in the winter and forward in the spring? Read on my friend. Its everything you've ever wanted to know about Daylight savings Time.

Thanks to our planet's cockeyed position relative to the sun, residents of the latitude-disadvantaged Pacific Northwest will set their clocks to "fall back" an hour this weekend to shift our shrinking allotment of winter light to the morning side by taking it away from the end of the day.

The time change was altered by federal legislation to persist for one month longer this year, based on the debatable presumption that this will reduce energy consumption by about 1 percent. It goes into effect at 2 a.m. Sunday.

The change stems from an energy bill that lengthened daylight saving by four weeks. It kicked in this year with clocks rolling ahead by one hour on the second Sunday in March, rather than the first Sunday of April. They'd typically be set back on the last Sunday in October, but that changed, too, to the first Sunday in November.

Scientists say this twice-a-year manipulation of time, whether on a new schedule or not, definitely has some downsides. This is largely due to our body's multiple biological clocks, which evolved to operate according to the sun's behavior.

"Morning light is the most important light for synchronizing our circadian rhythms," said Dr. David Avery, a psychiatrist at the University of Washington who specializes in studying the connection between light, sleep and depression. Circadian rhythm refers to the 24-hour cycle for life on Earth.

When daylight-saving time is in effect and reduces the amount of morning light, Avery said, the risk of seasonal depression in some people increases. He said traffic accidents might also be expected to increase as morning commuters struggle against biology.

"It's not natural to wake up in the dark," he said. "What our ancestors did was wake up at dawn, whenever dawn came."

This, Avery said, is hardwired into our brain and it doesn't simply adjust in our bodies when we adjust the alarm clock.

"From a biological point of view, it really doesn't make any sense to do daylight-saving time," agreed Horacio de la Iglesia, a UW neurobiologist who studies how the brain governs some of the other biological clocks in the body.

Most people know the brain operates according to a biological clock on this 24-hour solar cycle. De la Iglesia has shown that the human body actually depends upon many such clocks, a coordinated network that needs to work in synchronicity.

"There are biological clocks in the liver, lungs and other organs as well," he said. "We have these circadian rhythms because they allow the body to anticipate cyclical events."

For example, he said, the adrenal gland releases the stress hormone cortisol before you wake up every morning to move the stored sugar, glucose, from the cells into the bloodstream.

"That helps get you going," de la Iglesia said. Some of these biological clocks can adjust fairly rapidly to changes in the light-dark cycle (recovering from jet lag, for example) but others appear to persist longer, he said.

Woodruff Sullivan, a UW astronomer who spends a lot of time thinking about time, agreed that shifting clock time back and forth an hour twice a year is not really necessary. But because Sullivan regards clock time in general as hardly natural, he figures one more manipulation is OK.

"I already have pretty weird hours," he said. "I like the idea of shifting daylight to fit when people are up."

The reason those of us living in the northern latitude have less daylight in winter (and more in summer), Sullivan noted, is because the Earth is tilted relative to the sun. As it moves around the sun in its orbit, the planet in summer is tilted so that the northern latitude gets more daylight. In winter, it's tilted away and gets less daylight for every 24 hours.

Clock time didn't really exist for most people until the early 19th century, Sullivan said. Time before then was purely a local thing, he said, set by the movement of the sun.

"A sundial gave them local solar time," said Sullivan, who happens to be a big fan of sundials

For many years, Sullivan has helped install sundials throughout the Northwest and other parts of the world -- and even on another world. The UW astronomer, along with popular science personality Bill Nye, convinced NASA to put a sundial on its Mars rovers, Spirit and Opportunity.

From a scientific standpoint, daylight-saving time, the maps showing time zones with hard boundaries and the concept of "coordinated universal time" (previously, Greenwich Mean Time) are in concept actually no less arbitrary than the decision by some communities to not play by these rules. Arizona and Hawaii, for example, don't observe daylight-saving time.

Despite the potential adverse health effects of changing the clocks, Avery said he doesn't see most communities in the northern latitudes seeking to abandon the convention.

"If we were to remain on Pacific Standard Time year-round, from June 11 to June 21 the sun would rise at about 4 a.m. and set at approximately 8 in the evening," he said. "That wouldn't be good."

Avery said his primary concern is with the timing and one-month extension of this year's approach to shifting the clock. The net effect, he said, is that there will be more days of morning darkness this year come spring.

As a doctor, he recommended that those who find this change difficult turn on the lights upon awakening and turn them down before retiring in the evening. The dark-light cycle, Avery said, can be adjusted to some extent.

And stop staring at your "Microsoft Blue" computer screen late at night, he said. Blue light appears to suppress the hormone melatonin, Avery said, which is released by the body to induce sleep.

"I've changed my screen background to orange, which subtracts blue light," Avery said.



Remember to turn your clocks back one hour before going to bed on Saturday night.


Summer solstice: The longest day was June 21 at 15 hours, 59 minutes of daylight.

Winter solstice: The shortest day will be Dec. 21 at eight hours, 25 minutes of daylight.

1784: Benjamin Franklin first mentioned the idea of daylight-saving time in his essay "An Economical Project for Diminishing the Cost of Light."

1840: "Standard time" was first established in England to regulate the railroads.

1883: Railroads in the United States instituted standard time with time zones.

WWI: Changing between standard time and daylight-saving time began with World War I.

1916: British summer time was instituted in 1916, when clocks were put one hour ahead of Greenwich Mean Time.

1918: The U.S. followed with DST to save money for military efforts during World War I. The move was so unpopular, it wasn't brought up again until World War II.

1942: From then on, DST has been followed by the majority of the United States.

Source: National Weather Service, Albany Times Union
[via http://seattlepi.nwsource.com]

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