The most abundant, substantial objects in the Solar System are the comets of the Oort Cloud, a roughly spherical shell that begins at three times the distance of Pluto's orbit and extends about halfway to the nearest stars. According to current estimates, there are about six trillion comets in the Oort Cloud.

From the distance of the Oort cloud, the sun is a bright star, about as bright as Venus looks from Earth. The temperature there is only four degrees Kelvin, which is about as cold as gets in the natural universe.

Once in a while, an Oort comet falls into the inner solar system. These rare visitors are interesting to science because they represent a sample of conditions as they were in the earliest stages of formation of the solar system.

More about the Oort Cloud:
http://www.windows.umich.edu/cgi-bin/tour_def/comets/Oort_cloud.html
http://zebu.uoregon.edu/~js/glossary/oort_cloud.html
http://www.amsci.org/amsci/issues/sciobs97/cloud.html
http://www-hpcc.astro.washington.edu/mirrors/nineplanets/kboc.html

On the average, a normal person's eye muscles move about 100,000 to 150,000 times in one day. During the daytime, our eyes move as often as three or four times per second, while in the deepest sleep they hardly move at all. Our eyes must move that fast because there is only one tiny area on our retina that is able to see any real detail. With each movement that tiny area, which is called the fovea, can see another little bit of detail to build up a larger picture. With our eyes moving that often, why don't we see a sequence of rapidly flickering images? Our brains are experts at combining the fast-changing images into a whole, so that we see a complete view even as our eyes scan around rapidly.

How would the world look if your brain could not fuse the images?

Watch a flickering movie and see what the retina's image really looks like: http://www.klab.caltech.edu/~itti/retina/

An experiment to see the retina of your own eye: http://www.exploratorium.edu/snacks/seeing_retina

A teddy bear is a furry stuffed bear, usually a child's toy. The toy and its name were born together after a celebrated act of compassion by U. S. President Theodore "Teddy" Roosevelt.

There are several versions of the story. In the most popular one, Roosevelt went on a bear hunting trip in November 1902, but no bear was bagged. To give the President a chance for some kind of trophy, someone tied a bear cub to a tree so he could shoot it. He refused.

Soon after, a cartoon was published in the Washington Post depicting the incident, and there was a great popular outcry in favor of the President's thoughtful restraint. An enterprising businessman began selling stuffed "Teddy bears," and they became an instant hit.

History of the teddy bear, including other versions of the story: http://www.arts.unimelb.edu.au/amu/ucr/student/1997/chiba/tbh.htm

Teddy bears have now been honored on postage stamps: http://www.usps.gov/kids/stompfeature49.html

Today's Person Of The Day is Teddy Roosevelt: http://www.LearningKingdom.com/person/archive/2000/02/18.html

Every day, more than 1,000 gallons of water are lost into space from the top of Earth's atmosphere. Most of the water is lost near the magnetic poles, where charged particles from the Sun split water molecules into electrically charged hydrogen and oxygen ions.

The charged ions move in paths that follow the lines of Earth's magnetic field. Since that field points straight up near the poles, they can escape there. The amount lost can be much larger during solar storms when the solar wind becomes more powerful. If Earth had no magnetic field, the amount lost would be far greater and the oceans would have evaporated millions of years ago.

Scientists suspect that a similar mechanism might have removed water from the atmospheres of Mars and Venus, both very dry planets today.

How Earth's magnetic field protects the atmosphere (and us!): http://wwwssl.msfc.nasa.gov/ssl/pad/sppb/edu/magnetosphere/mag4.html

The Polar spacecraft measures the "auroral fountain" of ions: http://wwwssl.msfc.nasa.gov/newhome/headlines/ast08dec98_1.htm

Cool Facts about auroras, also produced by streams of charged particles: http://www.cool-fact.com/archive/1997/07/10.html
http://www.cool-fact.com/archive/1998/01/19.html
http://www.cool-fact.com/archive/1999/12/30.html

Almost everyone has experienced a muscle cramp. The muscle becomes contracted and rigid, and is usually quite painful. The contracted muscle gets locked into a self-sustaining knot, which can last for hours or days.

Many muscle cramps are associated with exercise. These cramps are often due to a depletion or imbalance of salts in the muscle tissue, especially calcium, sodium, and potassium, which are lost in our sweat. A buildup of lactic acid, one of the byproducts of heavy exercise, also can contribute to the cramping. Such cramps can often be relieved by drinking "electrolyte" drinks that restore the salt balance.

If you get a cramp, it may be helpful to move the muscle into its least extended (shortest) position and massage it very gently. Eat something with sodium and potassium (like a banana) and wait for the cramp to ease.

More about muscle cramps: http://www.covenanthealth.com/features/health/sports/spor3206.htm

Tips for safe exercise, and advice for various sports injuries: http://cpmcnet.columbia.edu/texts/guide/hmg24_0002.html

More Cool Facts about muscles:
http://www.cool-fact.com/archive/1998/08/26.html
http://www.cool-fact.com/archive/1998/09/10.html
http://www.cool-fact.com/archive/1999/08/16.html

In 1911 a Dutch physicist named Heike Kamerlingh Onnes noticed that when he cooled mercury metal to a temperature just above absolute zero its electrical resistance completely disappeared. He had discovered superconductivity, a property that some materials have at very low temperatures.

When all electrical resistance disappears, some strange things happen. Electric currents can flow forever in closed loops through the material. External magnetic fields cannot enter because they cause exactly equal and opposite currents to flow, repelling them.

Scientists are still trying to understand superconductivity. One of the great mysteries is whether there are materials that can show superconductivity at high temperatures. New superconducting materials are discovered every year, but so far they all must be cooled to very low temperatures before they become superconductors.

All about superconductors: http://superconductors.org/

Until 1993, the largest light telescope in the world was the 200-inch (5-meter) Hale Telescope at the top of Mt. Palomar in southern California. With its huge single-piece glass mirror, it was a tremendous feat of engineering.

In 1993, the gigantic 400-inch (ten-meter) Keck I Telescope was completed. At the top of Hawaii's dormant Mauna Kea volcano, it is eight stories tall and weighs 300 tons. In 1996 its twin, the Keck II, was brought online.

Instead of a single continuous mirror, each Keck Telescope has thirty-six thin hexagonal segments that can be individually aligned for maximum accuracy. With its huge collecting area, each Keck can gather forty thousand times as much light as the telescope that Galileo used.

The twin Keck Telescopes: http://www2.keck.hawaii.edu:3636/realpublic/gen_info/gen_info.html

More Cool Facts about telescopes and other seeing instruments:
http://www.cool-fact.com/archive/1998/04/13.html
http://www.cool-fact.com/archive/1998/11/17.html
http://www.cool-fact.com/archive/1999/08/03.html

March 10, 1982 The "Jupiter Effect" took place, during which all the planets of our solar system became aligned. In the 1970s it was hypothesized that the alignment would cause earthquakes and other catastrophes. The date came and went and nothing happened.

On May 5, 2000, another planetary alignment is suppose to take place, and once again, apocalyptic visions have been pronounced.

May 05, 2000: Planetary Alignment And Its Destructive Potential

Have you seen seagulls or migrating geese flying in a "V"? Through evolution, flocks of birds have spontaneously developed the best instinctive strategy for long-distance flight as a group.

Freeway drivers may be familiar with the "wake effect" that reduces gas usage when one follows just behind and to one side of a large truck. The "V" flying flock takes advantage of exactly the same effect.

By flying in a "V", birds minimize the energy used by the whole flock to get where it's going. Recent research shows that even the leader of the "V" benefits from the formation. A "V" flock of 25 birds can travel 70% farther than an unformed flock, and it also flies faster.

More about formation flying by flocks: http://www.gi.alaska.edu/ScienceForum/ASF12/1248.html

Even today, bird flight is still quite mysterious: http://www.nwf.org/nwf/natlwild/flight.html

More Cool Facts about flying birds:
http://www.cool-fact.com/archive/1997/07/30.html
http://www.cool-fact.com/archive/1998/01/16.html
http://www.cool-fact.com/archive/1998/09/30.html

Although freeway traffic flow is very complex, science is beginning to reveal its dynamics. It turns out to have distinct states, like the gas, liquid, and solid states of matter. When traffic moves like a gas, the cars are far enough apart that each one can move freely without much affecting its neighbors. Drivers instinctively maintain large separations, and traffic flows at maximum speed. When things get a little busier, cars slot together into clusters that travel only a little slower than they do in the gas state. The clusters are like condensed droplets of liquid, and they are separated by intervals of gaseous traffic. If traffic gets even heavier, another transition happens. The traffic enters a thick, viscous state like honey or tar. If it gets much heavier you have gridlock, the solid state of traffic flow.

Computers make the study of "traffodynamics" easier:
http://www.sciencenews.org/sn_arc99/7_3_99/bob1.htm

The curious musings of a traffic psychologist:
http://www.aloha.net/~dyc/ch14.html

More Cool Facts about transportation:
http://www.cool-fact.com/archive/1998/11/05.html
http://www.cool-fact.com/archive/1999/12/07.html
http://www.cool-fact.com/archive/2000/01/28.html

Teflon, or polytetraflouroethylene, (PTFE) is one of the most inert substances known. It's so inert that nothing sticks to it; to stick, it would have to react in some way. So how does it stick onto the surface of a frying pan?

In early days, the Teflon was pressed onto the metal surface after the metal had been "roughed up" by abrasion and coated with a primer chemical with lots of microscopic cavities. The Teflon squeezed into the cavities and stuck to the pan by sheer mechanical strength. But those early frying pans didn't keep their coating very long, because Teflon is so inert that its long molecules slither like wet spaghetti, and it often came loose from the mechanical primer.

Modern non-stick pans are made with a much more sophisticated process. Parts of the Teflon molecules at the bottom of the coating have different side chains that actually stick to the metal, while the upper ends of the molecules are pure Teflon. The layer sticks on the bottom, but not on top.

More about how they make it stay stuck:
http://more.abcnews.go.com/sections/tech/Geek/geek990118.html

Teflon is a registered trademark of DuPont Corporation:
http://www.dupont.com/teflon