Image: Daylight saving
Chris Gardner  /  AP
Clock conservator Eric Wilson makes adjustments to The Rittenhouse Clock in the Westphal Picture Gallery at Drexel University in Philadelphia. The clock, built in 1773 by astronomer David Ritenhouse, has 16 sets of chimes and plays 10 tunes.
updated 11/4/2011 9:17:29 AM ET 2011-11-04T13:17:29

If you've been falling behind on sleep, this is the weekend to fall back into bed for an extra hour — and take advantage of the transition from daylight saving time to standard time.

The time change is part of a longstanding tradition, in which most Americans push their clocks ahead an hour in the spring ("spring forward") and turn them back an hour in autumn ("fall back"). The change officially takes place at 2 a.m. daylight saving time on Sunday, Nov. 6 (which instantly becomes 1 a.m. standard time).

A few years ago, lawmakers shifted the schedule slightly, setting the changeover for the first Sunday of November rather than the last Sunday of October. The goal was to extend the energy savings that are thought to result from daylight saving time.

The idea behind daylight saving time — or summer time, as it's known in other parts of the world — is to use the extended daylight hours during the warmest part of the year to best advantage. Timekeepers shift some of that extra sun time from the early morning (when timekeepers need their shut-eye) to the evening (when they play softball).

The shift reduces the need for lighting during the evening, and that's why daylight saving time is considered an energy-saver — that is, as long as there is morning sunlight to spare. Now that dawn is coming later and later, the daylight-saving advantage has largely dissipated

With the clocks turned back, it will be lighter (or at least less dark) in the morning, but darkness will fall earlier in the evening.

Not everybody goes along with the daylight-saving plan. Arizona and Hawaii, for example, stay on standard time all year round. Each state or country comes up with its own schedule for the switch, and that schedule may be subject to change.

Around the world, Canada and the members of the European Union operate similar summer-time shifts. Most European countries made the shift to standard time last weekend, so in that sense America is just now catching up. And yes, some countries in the Southern Hemisphere move their clocks forward an hour at this time of year, in time for the coming summer there.

If you're in a fall-back time zone, you'll want to savor that extra hour of shut-eye: A major study released by the National Center for Health Statistics indicated that sleep deprivation was linked to all sorts of health problems, including smoking and obesity.

Here are more questions and answers about the science of sleep:

When we wake up, why do we have crust in our eyes? - S.S.
“Eye crusts” are the leftover protein and fat from tears that have dried up. Tears have three components:

  • Salty water, which comes from the tear gland behind the upper outer corner of our eye.
  • Protein, secreted by the conjuctiva, which is the clear film that covers the eye.
  • And fat, which comes from ducts in the eyelids.

Tears do lots of jobs. They clean the eye. They fill in tiny imperfections in the surface of the cornea, which needs to be perfectly smooth for maximal vision. They also deliver nutrients to the cornea, which has to be clear to let light through to the iris, and therefore has no blood vessels to deliver a “food supply.” And of course tears flow at times of emotion, when the tear glands power up and produce more salt water.

At night, with our eyes closed and protected, we don’t display emotion, and with our eyes closed we don’t get dirt in our eyes. So we don’t make tears. Small amounts of the mixture already on the surface of the eye seep out, but without a fresh supply of liquid from the tear gland, the fat and protein dry up.

Why does your breath smell so bad when you wake up? - S.B. and A.B.
This one ought to get you to brush before you go to bed. That smell is ... bacteria gas. Gross, but accurate. There are lots of bacteria in our mouth all the time, feeding on the tiny leftover bits of what we’ve eaten. Ever hear of plaque, the stuff all those toothpaste ads promise to get rid of? Plaque is nothing more than organized colonies of bacteria chowing down on food bits on your teeth.

When we’re awake, some plaque is removed when we chew, talk, drink, even when we breathe. But overnight, when those disturbances in the mouth stop, it’s party time for the bacterial colonies on your teeth, and they multiply like crazy. Their waste products are acids, which cause cavities, and gases, which cause that rude blast of morning breath.

Why do we snore? - S.D.
To bug the person sleeping next to us, of course.

Actually, there are several causes of snoring. All of them have something to do with restriction of the upper airway.

  • Kids with swollen tonsils or adenoid glands snore.
  • People sleeping on their back snore because the tissues in the neck are pressing down on the windpipe.
  • Overweight people snore for pretty much the same reason, or because some of their fat is stored in tissues in the neck.
  • People with colds snore because they have swollen sinus tissues in their throat.
  • Drinking alcohol causes snoring by relaxing the muscles in the throat, which restricts the size of the airway.
  • We snore more as we age because of the loss of elasticity in neck tissues, which sag in on the windpipe.
  • People with misshapen jaws, larger-than-normal tongues, or on relaxant medications, all are more prone to snore.

So if you try to sleep next to an overweight elderly drunk with a misshapen jaw and a cold who’s taking muscle relaxants ... bring industrial-strength earplugs.

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Why is yawning contagious? - P.H.
If you don’t think YAWNING is contagious, see if you YAWN by the time you’re done reading this explanation of YAWNING.

First, let’s dispel a myth. You don’t yawn to take in extra oxygen. “That’s been rejected in lab tests,” says YAWN expert Robert Provine, professor of psychology at the University of Maryland’s Baltimore County campus. He had test subjects breathe air with extra oxygen. For others, he reduced the oxygen intake by giving them air high in carbon dioxide. Neither caused more or less YAWNING.


Provine says “we YAWN when we’re changing states of activity. Going from sleep to wakefulness, like YAWNING in the morning. Or wakefulness to sleep.” (He says we YAWN more in the morning when we wake up, by the way.)

“Concert pianists will YAWN before going out to an important performance. Olympic athletes YAWN before the big event. Embryos begin YAWNING eleven weeks after conception,” Provine notes. He says YAWNING is somehow connected to changing levels of body activity, changes from one state to another, like inactive to active or vice versa, but nobody understands just what the connection is.

“It probably helps stir up the blood and brain chemistry to facilitate those transitions from one level of activity to another.”

Why? “YAWNING is ancient and autonomic,” Provine says. “Maybe it’s to get everyone in the tribe to synchronize their states of activity, to increase the success of the tribe if everyone’s working together. We really don’t know.”


YAWNING is highly contagious, he says. Every vertebrate species YAWNS. Fish YAWN. Birds YAWN. Alligators YAWN. But Provine says it’s apparently only contagious in humans.

Provine has made test subjects YAWN by showing them a YAWNING face. Interestingly, if he shows them just the YAWNING mouth, it doesn’t trigger the YAWNING. If he covers the mouth, and shows them just the nose and eyes of the YAWNING face, it does. He’s made subjects YAWN by talking about YAWNING, or asking the test subjects to think about YAWNING, or by having them read about YAWNING.

Yawning yet?

Alan Boyle is's science editor. David Ropeik is a risk communication consultant who provided information for this report in 2000.

© 2013 Reprints

Interactive: Sleep science

Explainer: The science of fall

  • Jacek Turczyk  /  EPA

    These are the sights of fall: Leaves piled high in the yard, pumpkins engorged on vines, flu shots, bears fattening up, shooting stars and the harvest moon. Hurricanes wind down and the Santa Ana winds begin to blow. Voters head to the polls and Oktoberfest beers flow. What's the science behind all these sights? Click the "Next" arrow above to find out.

  • Foliage is a great unmasking

    Nancy Palmieri  /  AP

    Scientists describe fall foliage like a great unmasking. Throughout the spring and summer growing season, trees produce chlorophyll — a green pigment that captures the energy in sunlight. As the days shorten in late summer and early fall, cells between the leaf and stem form a corky layer that blocks the flow of nutrients. Chlorophyll production ceases, the green fades away, and the underlying yellow and orange pigments are revealed. Reds and purples are produced by sugars trapped in the leaves. Eventually, these pigments, too, break down, the leaves turn brown and fall to the ground.

  • Harvest moon helps get the crops in

    Rene Johnston  /  ZUMA Press file

    Of all the named full moons — and every full moon is named — perhaps the best known is the harvest moon. This is the full moon that falls closest to the fall equinox and allows farmers extra hours of light to finish the chores of reaping what they have sown. Contrary to popular belief, the harvest moon does not linger in the sky any longer than other full moons, notes syndicated columnist Joe Rao. Rather, on the days surrounding the full moon, the moon seems to rise at nearly the same time each night instead of the normal average of 50 minutes later each day. Other full moons this time of year include the beaver, or hunter's moon, which gives extra light to hunters, and the cold moon, which comes as winter's grip takes hold.

  • Time to get flu shots

    AFP-Getty Images

    Fall is flu shot time. Every year, starting in January, the world health community scours the planet for strains of the influenza virus most likely to cause an outbreak of the flu. Three prime candidates are selected, combined with a strain that is safe for humans, and injected to a fertilized chicken egg. There, the mixture evolves into a single strain that will prompt the human immune system to produce antibodies to fight all the included strains. This seed virus is sent to vaccine manufacturers, who produce more of the virus in fertilized eggs. This vaccine is then harvested, treated and packaged for distribution. By early fall, flu shots are available.

  • Bears fatten up for hibernation

    National Park Service

    For bears, fall is the time to feast on the remaining summer berries, fish and other snacks in order to fatten up for the long winter snooze known as hibernation. As the days get shorter, the mammals will scout out and excavate a den, perhaps in a cave or amidst thick vegetation on a hillside. In Yellowstone National Park, biologists report, a grizzly might remove up to a ton of material getting its den ready. As the weather turns chilly, bears will hang out in front of their dens, stop eating, turn lethargic, and decide to head for cover once the first major snowstorm hits.

  • Breeding a better pumpkin

    Monsanto via PR Newswire

    Halloween is a favorite fall holiday for many people, and no Halloween is complete without a perfect pumpkin. Leave it to researchers at a subsidiary of the agricultural giant Monsanto to make sure no witches and ghouls get upset. The company has selectively bred more than 10 commercial varieties of pumpkin, each with desirable traits such as a firm, green stem that doesn't easily snap off and a deep orange color. Despite Monsanto's reputation for making so-called "Frankenfoods," the company has no immediate plans to genetically engineer the pumpkin, a researcher told the Associated Press.

  • Hurricane season winds down


    Though it may seem like the biggest and baddest hurricanes form during the dog days of summer, hurricane season officially extends to the first of November. In fact, the first weeks of fall can serve up some doozies. Take Wilma, for example, an October 2005 storm that peaked as a Category 5, the highest level possible, before it weakened slightly and tore across Mexico's Yucatan Peninsula. The storm then headed north and cut across Florida as a Category 3.

  • Santa Ana winds crank up, fan flames

    Kevork Djansezian  /  AP

    In California, the famed Santa Ana winds crank up and can flame ferocious wildfires that sweep down from the wilderness into the suburban sprawl that spreads out from Los Angeles and San Diego. The winds are triggered by high pressure that builds up over the desert areas of the Great Basin, including Utah and Nevada. As the winds race downslope, they heat up. Fires tend to erupt in October because the winter rains have yet to soak California, giving ample dry fuel for the flames, according to atmospheric and ocean scientist Robert Fovell at the University of California at Los Angeles.

  • Science seeks support at the polls

    Don Farrall  /  Getty Images stock

    There's a whole branch of science dedicated to the study of politics, and many science buffs are dedicated to raising the profile of the sciences on the political stage. As the election season ramps up each fall, talking heads from across this spectrum take to the airwaves offering up analyses and stumping for their positions. In the 2008 presidential election cycle, for example, backers of the ScienceDebate 2008 initiative persuaded the political camps of candidates Barack Obama and John McCain to spell out their stances on issues ranging from stem cells and global warming to funding for basic science research and space exploration.

  • Leonid meteors put on a sky show

    Stephen Shaver  /  AFP - Getty Images file

    Each November, Earth passes through streams of dusty debris shed by comet 55P/Tempel-Tuttle that result in the meteor shower known as the Leonids. The shower was a veritable storm with up to 3,000 so-called shooting stars per hour in the late 1990s and early 2000s. Astronomers are predicting a half-storm of about 500 meteors per hour on Nov. 17, 2009, as Earth orbits through a stream of debris shed in 1466. The 1998 shower is shown here as seen over the Great Wall of China.

  • Energy policy and Oktoberfest beer prices

    Wolfgang Rattay  /  Reuters file

    Each fall, millions of people flood into Munich, Germany, for Oktoberfest to eat hearty foods and drink copious amounts of beer. In recent years, the price of a mug has risen, German brewers say, because farmers are planting less barley — the staple ingredient of beer — in favor of subsidized crops such as corn and rapeseed that are used to brew biofuels. While biofuels are considered in some circles as more eco-friendly than fossil fuels like coal and oil, some beer drinkers are pushing for an end to the subsidies that appear to be messing with the price of their suds.


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