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Natural World
How often do Earth's magnetic poles reverse?
What's the largest known nebula?
Where are the coldest volcanoes?
The brightest auroras in the solar system.
What happens when galaxies collide?
What were the largest crocodiles that ever lived?
The hottest volcanoes in the solar system.
What moon has the closest orbit to its planet?
Where is the coldest place on Earth?
How are diamonds formed?
Where is the largest temperate rain forest?
Why do birds fly in a "V" formation?
What color is pure water?
What part of the world has the most tornadoes?
What's the most powerful earthquake ever?
What were the largest birds that ever lived?
Are dogs really colorblind?
Are there people with internal mirror-image bodies?
What was the largest known lava flood?
Do stars ever collide?
How much Hydrogen does the Sun fuse every sec.?
Where is the longest known underground river?
How do we know the universe is expanding?
What color is pure water?
Will the milky Way Galaxy collide with another galaxy?
What are the conditions at the center of the Earth?
Where is the greatest diversity of fruit flies?
What are the smartest dogs?
How many times do our eyes move in one day?
What was the largest landslide in recorded history?
How do hunting spiders find their way home?
What is the only magnetic moon in the Solar System?
What's the longest river in the world?
What land animals had the largest skulls?
Has Niagara Falls ever been dry?
What US state is most densely forested?
When is the Earth closest to the Sun?
How does the Earth lose water?
What planet's surface has the most extreme climate?
What kind of spider steals food from other spiders?

Human Technology
Why is there no "Q" or "Z" on many telephones?
Why does a week have seven days?
How many languages are there in the world?
What's the fastest that humans have ever traveled?
How can a cricket be used as a thermometer?
What is a sonic boom?
What was the best throwing weapon before bows?
What's the oldest brand of carbonated drink?
Why did the Tower Of Pisa tilt to one side?
How did "qwerty" keyboards become standard?
Why will New Orleans will soon disapear?
What kind of fax machine makes 3D objects?
What's the hottest kind of flame?
Where are spider webs used as fishing nets?
How do workers in Bengal protect against tigers?
How long was an hour in ancient times?
How do spacewalking astronauts stay warm (or cool)?
What kind of cloth was made from part of a shellfish?
What was the first official U.S. coin?
What's the most powerful chemical explosive?
Can electronic devices be made out of plastic?
What is the secret of radar-absorbing paint?
Who invented rockets?
What was the first known use of the wheel?
Where is the world's largest airport?
How does the Global Positioning System work?
How did a map help stop an outbreak of cholera?
What kind of car flies through the air?
What kind of material has no electrical resistance?
What was the first animal sent into space?
How are large buildings protected against earthquakes?
What's the oldest printed book with a date?
How are construction cranes placed atop new buildings?
What year was missing ten days in October?
When were clock hands invented?
How are coins designed and produced?
Who made the first marbles?
What is the oldest board game in the world?
What's the oldest corporate entity in the world?
What is the largest construction project in the world?

How often do Earth's magnetic poles reverse?
The magnetic field of Earth is not constant. Not only does the magnetic pole wander slowly, every so often the entire magnetic field flips completely over. No one knows why this happens, although there are theories relating it to the movement of liquid iron deep inside the Earth.

Pole reversals happen at unpredictable intervals of 5000 years to nearly one million years. By studying the magnetic fields of rocks that solidified at various times in the past, scientists have been able to reconstruct the history of Earth's magnetic pole reversals.

Once that history was clear, it became possible to date certain rock formations by studying their magnetic fields. Together, these two approaches have helped us pin down the age of the Earth and the times of various events in its history.

What would happen if the magnetic poles reversed today? Reference1 - Reference1

Dating ancient objects using tree rings, magnetism, and atoms: Reference1

More Cool Facts about Earth's poles and magnetic field: Reference1 - Reference2 - Reference3

What's the largest known nebula?
The largest known nebula (cloud of gas and dust) is the Tarantula Nebula, named for its shape. More than 1000 light years across, it is one hundred times larger than the famous Orion Nebula.

The Tarantula Nebula is about 165,000 light years from Earth, in a small, nearby galaxy called the Large Magellanic Cloud. It's the only extra-galactic (outside of our galaxy) nebula that can be seen without a telescope. If it were as close as the Orion Nebula (about 1500 light years) it would be as wide as 60 full moons, and bright enough to cast shadows.

Nebulas like the Tarantula are the birthplaces of new stars, which collapse at the center of swirling whirlpools. Our solar system was probably born within such a nebula.

Pictures of the Tarantula Nebula: Reference 1 - Reference 2 - Reference 3

Where are the coldest volcanoes in the solar system?
Neptune's moon Triton is the coldest place in the solar system, with a surface temperature of -235 degrees Celsius (-390 degrees Fahrenheit). As cold as it is, there are active volcanoes on Triton in which the erupting liquid is frigidly cold liquid nitrogen.

At Triton's surface, nitrogen normally exists as frozen ice. But under the surface, where Triton is heated by slow radioactive decay of its rocks, nitrogen melts into a liquid. When the liquid heats up still further, it boils and erupts through the surface, spewing evaporating liquid nitrogen high into space.

Triton is one of the few moons in the solar system that has an atmosphere and clouds. The clouds, seen by Voyager 2, are evidence of Triton's volcanoes: Reference 1 - Reference 2

More Cool Facts about planets and moons: Reference 1 - Reference 2 - Reference 3

Where are the brightest auroras in the solar system?
Auroras (or aurorae) are glowing displays produced when charged particles stream down into a planet's atmosphere from space. The brightest auroras in the solar system are those of Jupiter, the largest planet, whose auroras are 1,000 times brighter than those of Earth.

Jupiter's auroras are made by particles from its highly active moon, Io. Volcanoes on Io spew electrons and other particles into the region around Jupiter, and they are funneled into Jupiter's polar regions by the planet's enormous magnetic field.

Recent studies have shown that Jupiter's auroras are connected to many other fascinating phenomena. There are mysterious "electrojets" of charged particles that race around the planet's poles faster than the speed of sound, and a strange "skirt" of particles that rotates with the planet.

Pictures of Jupiter's auroras, taken by the Hubble Space Telescope: Reference 1

More Cool Facts about auroras: Reference 1 - Reference 1

More about Io: Reference 1

What happens when galaxies collide?
The collision of two galaxies takes hundreds of millions of years. Galaxies do not actually crash into each other, because they are mostly empty space. Instead, they pass through each other, becoming distorted by gravitational interactions.

Even though colliding galaxies may contain hundreds of billions of stars, very few stars collide with each other or even come close, because the stars are so far apart relative to their size. But planets orbiting those stars might be tossed into new orbits by the gravity of passing stars.

As galaxies pass through each other, the gases they contain can heat up and collapse, forming "starburst" areas rich with bright new star systems. Colliding galaxies may merge into one larger galaxy, or pass completely through each other.

More about galactic collisions: Reference 1 - Reference 2

Computer simulation of colliding galaxies: Reference 1

More Cool Facts about galaxies: Reference 1 - Reference 2 - Reference 3

What were the largest crocodiles that ever lived?
According to the fossil record, the largest crocodilians that ever existed were the gigantic Deinosuchus ("terrible crocodile"), which lived during the late Cretaceous (85 to 66 million years ago). These giant semi-aquatic predators may have grown as long as 15 meters (50 feet).

During that time, a shallow sea called Tethys covered much of what is now the central United States. Deinosuchus lived in swamps and estuaries along the edges of the Tethys Sea, where it was probably able to capture and devour even large dinosaurs.

Deinosuchus was a distant ancestor of modern crocodiles and alligators. Few fossils of it have been found, but one skull is almost six feet long (two meters).

How big were they? Check out these paintings: Reference 1

More about Deinosuchus: Reference 1 - Reference 2

More about crocodilians: Reference 1

More Cool Facts about giant reptiles: Reference 1 - Reference 2 - Reference 3

Where are the hottest volcanoes in the solar system?
The hottest known volcanoes are on Jupiter's moon, Io. The lava that emerges from Io's volcanoes can be as hot as 1800 degrees Kelvin (1527 degrees Centigrade), about one third as hot as the surface of the Sun.

The heat of Io's volcanoes is generated by the tidal flexing of the moon under the gravitational stress of Jupiter and two of its other moons, Europa and Ganymede. As Io orbits Jupiter it changes shape slightly, and its interior is heated.

Although Io's interior is utra-hot, its surface is very cold. Gas emitted from the volcanoes arcs high into the vacuum of space, where it freezes into fine snow and falls back down to Io, coating its surface with multicolored deposits.

More about Io and its super-hot volcanoes: Reference 1

More Cool Facts about volcanoes: Reference 1 - Reference 2 - Reference 3

What moon has the closest orbit to its planet?
Of all the moons in the solar system, the one with the closest orbit is Phobos, the larger of the two satellites of Mars. The orbit of Phobos is less than 6000 kilometers above the surface of the planet (3700 miles).

Phobos is an irregularly shaped chunk of rock and ice about 27 kilometers long (17 miles). Because its orbit is so low, it can only be seen from a limited strip of the planet near its orbital path. Seen from that strip, it crosses the sky quickly from west to east, twice a day.

Phobos' orbit is so low that tidal forces are pulling it closer and closer to Mars. Scientists expect that in about 50 million years it will either crash into the planet or break up into a thin ring of orbiting debris.

Phobos and Mars' other moon, Deimos, are thought to be captured asteroids: Reference 1

More Cool Facts about Mars: Reference 1 - Reference 2 - Reference 3

Where is the coldest place on Earth?
The coldest natural outdoor temperature ever recorded (as of January, 2000) was at Russia's Vostock Station in Antarctica. In 1997 the temperature there fell to -91 degrees Celsius (-132 degrees F). At this temperature, steel becomes so brittle it shatters easily.

Vostok Station is located in the middle of a vast expanse of uninterrupted ice, on a high plateau about 780 miles (1260 km) from the South Pole. The ice at Vostok is about 3700 meters thick (12,100 feet) and the surface elevation is 3488 meters (11,444 feet).

Vostok Station is not only the coldest place on Earth, it is also one of the driest. Because the air is so cold, it can hold very little moisture. The air's absolute humidity at Vostok is lower than that of the Sahara Desert.

More about Antarctica, by a scientist who spent a year at the South Pole: Reference 1

More Cool Facts about Antarctica: Reference 1 - Reference 2 - Reference 3

How are diamonds formed?
Natural diamonds are formed at least 150 kilometers deep in the Earth (93 miles) where the heat and pressure are great enough to squeeze carbon atoms together into the diamonds' tight crystal structure.

How do they get to the surface? Almost all diamonds mined today are collected from "diamond pipes," deep channels of a kind of volcanic rock called kimberlite or blueground. These structures started as nearly vertical columns of magma that pushed their way up carrying diamonds formed much deeper, and solidified in place. The most well known kimberlite pipes are in South Africa.

Most mined diamonds are of low quality, suitable for use in industrial abrasives. These are called "boart." The gem quality stones are only 15 to 20 percent of those mined.

A diamond in its original kimberlite matrix: Reference 1

More about diamond mining in South Africa: Reference 1

More Cool Facts about diamonds: Reference 1 - Reference 2

Where is the largest temperate rain forest?
The largest unbroken temperate rain forest in the world is the Tongass in southeast Alaska. It is 17 million acres of magnificent wilderness with abundant birds, bears, and other life. How wild is it? Surrounded by the Tongass, the city of Juneau (Alaska's capital) is accessible by ferries or by air, but not by roads.

The Tongass was extensively logged until the early 1990s, when the lumber mills began to shut down. Today, almost the entire region is protected from further development or exploitation, and many groups act to further that protection.

Temperate rain forests (those outside the tropics) look different than tropical rain forests. Dominated by coniferous trees, they grow more slowly but have a larger biomass (total mass of living matter) than tropical rain forests.

More about the Tongass: Reference 1 - Reference 2

Resource pages for protection of the Tongass: Reference 1 - Reference 2

More Cool Facts about forests: Reference 1 - Reference 2

Why do birds fly in a "V" formation?
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.

This works becuase a bird behind (diagonally) to another bird benefits from the air that is pushed down from the bird in front of it. This eases the drag of wind resistance for the birds in back and lets them fly longer without getting tired. When the front most bird gets tired, he/she rotates back and lets another bird take the lead.

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: Reference 1

Even today, bird flight is still quite mysterious: Reference 1

More Cool Facts about flying birds: Reference 1 - Reference 2 - Reference 3

What color is pure water?
You might think that absolutely pure water would be perfectly clear and utterly transparent, but it's actually blue. The blue color of the water in the oceans (and not the blue of the sky) is the reason why Earth is mostly blue as seen from space.

Pure water absorbs some of the light that passes through it. It absorbs red light more than yellow, yellow more than green, and green more than blue. Only the deepest blue light can travel very far through water, so a large mass of water takes on a deep blue color.

The blueness of water is easily visible in a swimming pool lined with white concrete. It's even visible in a white porcelain bathtub. But the bluest water of all is the clear tropical ocean far from land, where the sea is much bluer than the sky.

In essence, pure water is blue because water has a hard time absorbing the wavelength of blue light. Therefore, the blue color is mostly reflected from water while other wavelengths (associated with other colors) are absorbed by water.

The color of the ocean is strongly affected by plankton and impurities: Reference 1 - Reference 2

More Cool Facts about water: Reference 1 - Reference 2 - Reference 3

What part of the world has the most tornadoes?
The country with the most tornadoes is the United States, where about 800 twisters touch down every year. Most of them happen in the central plains states ("Tornado Alley"), where gigantic "supercell" thunderstorms sweep across the landscape, fed by moisture from the Gulf Of Mexico colliding with cooler, dryer air from the Rocky Mountains.

The second place winner for most tornadoes is Australia, where a few hundred form every year. They also happen sometimes in the plains of Asia.

Tornadoes can happen in any country that gets thunderstorms, but they require very special conditions. A heavy layer of cool, dry air must flow above a layer of warm, moist air, and there must be a certain twist to the air currents to start the vortex spinning.

The National Weather Service's page on tornadoes: Reference 1

More Cool Facts about thunderstorms: Reference 1 - Reference 2 - Reference 3

What was the most powerful earthquake ever recorded?
On May 22, 1960 an earthquake measuring magnitude 9.5 on the Richter scale struck southern Chile. The largest recorded quake was part of a week of disasters caused by slipping of two plates of the Earth's crust against each other.

One of the side effects of the earthquake was a tsunami (ocean wave) that swept across the Pacific Ocean at the speed of a jet airliner and caused deaths as far away as Hawaii and Japan. Large areas of Chile subsided by hundreds of feet. Six dormant volcanoes erupted and two new ones were born.

Earthquakes like the 1960 Chile mega-quake are caused at places where one part of the Earth's crust slips below another. This kind of quake, which does not happen often, can involve a very large section of the crust. Such quakes are not limited to Chile; they can also occur near the Pacific Northwest of North America.

More about the disastrous week in May 1960: Reference 1

An earthquake's magnitude reflects its strength: Reference 1

The most powerful quakes recorded in the USA: Reference 1

Tsunamis are the fastest, most dangerous ocean waves: Reference 1

What were the largest birds that ever lived?
When humans first came to the island of Madagascar around 600 AD, it was home to the largest birds that ever lived, the giant, flightless elephant birds (Aepyornis maximus). The last one probably died about 800 years ago.

The liquid capacity of one elephant bird egg was about two gallons (7.5 liters), 180 times that of a chicken egg, possibly making it the largest single cell ever. An adult bird probably weighed about one thousand pounds (450 kilograms). Like their living cousins the ostriches, they were running birds with thick, muscular legs and vestigial wings.

The elephant birds were among many species of large animals that disappeared from Madagascar after humans arrived. Today, the island's animal life is much reduced. Destruction of habitat has eliminated many species, and many more are threatened.

More about the gigantic elephant bird: Reference 1

The elephant bird was a ratite: Reference 1

Cool Facts about ostriches, the largest surviving birds: Reference 1 - Reference 2

Are dogs really colorblind?
It is not true that dogs are completely colorblind. While dogs do not have the same color vision as humans, they are able to tell yellow from blue. Like a human with red-green colorblindness, they can't tell the difference between red and green.

The reason for this limited range, in both the colorblind human and the dog, is that there are only two kinds of color receptors in the retinas of their eyes. While most humans have three kinds of color cells, with three different receptor molecules sensitive to blue, greenish-yellow, and red, dogs only have receptors for yellow and greenish-blue.

Canine eyes also lack another human trait: the fovea, an area especially dense with detail-sensing cells. As a result, their detail vision is not as good as ours. But they make up for this by having much better night vision and greater sensitivity to movement.

More about canine vision: Reference 1 - Reference 2

Dogs were the first animals to be domesticated: Reference 1

Are there people with mirror-image bodies?
About one person in 8,500 has a condition called situs inversus in which all the internal organs are located in mirror-image to the usual arrangement. People with situs inversus have their heart on the right and their liver on the left. The condition does not usually result in any medical problems.

No one knows why some people are internally flip-flopped, but recently scientists have discovered some clues.

In the earliest days of embryo development there is a critical period during which cilia (tiny beating hairs) cause a current to flow across the embryo. This current carries certain substances to one side more than the other, creating a left-right difference that becomes amplified into the left-right positions of the organs. People with situs inversus may have a genetic quirk that reverses or removes that current.

The left and right lungs different sizes: Reference 1

More about situs inversus: Reference 1

Another rare genetic condition: Reference 1

What was the largest known lava flood?
The largest known outpouring of lava on Earth happened when the giant supercontinent of Pangaea split apart. The split formed what is today the Atlantic Ocean, and separated Africa and Europe from North and South America. This happened at the end of the Triassic Period, at the same time as one of Earth's largest (and least understood) mass extinction events.<> This extraordinary flood of lava covered an area of seven million square kilometers (2,700,000 square miles) and may have released enough carbon dioxide to dramatically alter the planet's climate. We don't know yet whether the eruptions caused the mass extinction, but it is considered likely.

Today, remnants of that ancient lava flood can be found at New York's Palisades basalt cliffs, as well as many locations in North and South America and Africa.

Article about the extinction (written before the lava flood's size was known): Reference 1

Article reporting the giant lava flood and its probable results: Reference 1

Lava sometimes explodes: Reference 1

Do stars ever collide?
In most parts of a galaxy the stars are so far apart that even when galaxies merge, the stars glide past each other without colliding. But there are two places where the stars are much closer together: in the central cores of galaxies, and in the cores of ancient globular star clusters.

A cloud of globular star clusters, the largest of which contain a million stars, surrounds spiral galaxies, like our Milky Way. A recent study of globular clusters shows that stars in the densest central regions can indeed collide, forming new stars called "blue stragglers."

Many blue stragglers are more than twice as heavy as other stars in the cluster, and spin much more rapidly. They also burn more brightly, making them look younger than the cluster, which can be billions of years old. This is evidence that the stars come from collisions, since new stars generally don't form within globular clusters.

Blue stragglers in cluster NGC 6397: Reference 1

This observation of a blue straggler by the Hubble Telescope demonstrates that a collision had occurred: Reference 1

Most stars in globular clusters are extremely ancient: Reference 1

How much hydrogen does the Sun fuse every second?
Every second, the Sun fuses about 700 million tons of hydrogen into helium. In the process, about five million tons of mass are converted directly into energy, which slowly makes its way out to the surface where it is radiated into space.

The conversion takes place near the innermost core of the Sun where the temperature is almost 16 million degrees Celsius (28.8 million degrees F). There, the same reaction that powers hydrogen bombs keeps the Sun inflated, preventing it from collapsing.

Our Sun has been burning hydrogen for more than four billion years, and it will keep doing so for several more billions of years. As a "main sequence" star its output is steady and predictable, which is good for life on its third planet.

The anatomy of the Sun: Reference 1

Read about what's actually happening in the core: Reference 1

Another Cool Fact about the Sun's energy production: Reference 1

Where is the longest known underground river?
The longest known underground river was recently discovered in the remote mountains of Vietnam. It's the Son Trach River, which runs underground for an astonishing seven miles (11 km) through a gigantic cave called Hang Khe Rhy (Grass Stream Cave).

The expedition that discovered and partially mapped the Son Trach River spent twelve days underground, plunging through ice-cold rushing water and painstakingly mapping every curve and grotto they found.

Son Trach River and Hang Khe Rhy cave form part of the Phong Nha massif, a geological unit that contains some of the world's most spectacular karst limestone formations. The caves, passages, and above-ground formations in karst areas are formed by the action of water, which dissolves parts of the rock while leaving other parts behind.

The discovery of Son Trach River: Reference 1

A guide to caves in Vietnam, curiously translated: Reference 1

Today's Cool Word is karst: Reference 1

More Cool Facts about caves: Reference 1 - Reference 2 - Reference 3

How do we know the universe is expanding?
Astronomers see countless galaxies for billions of light years in every direction. The farther away a galaxy is, the faster it moves away from us. The whole universe is expanding. How do we know?

When an object moves away from an observer, the light from that object changes color, similar to the way a train whistle changes pitch if the train is moving away. This "Doppler shift" causes the light of receding galaxies to stretch out, becoming more reddish. Measuring this "red shift," astronomers can tell how fast each galaxy is receding.

If the universe is currently expanding, it makes sense that at one time it was much smaller. The "Big Bang" theory, which describes how the universe might have started in a stupendous explosion, is one possible explanation of how the universe began.

The Hubble Constant is a number for how fast the universe is expanding: Reference 1

How big is the universe? Reference 1

More evidence for the Big Bang theory: Reference 1

What color is pure water?
You might think that absolutely pure water would be perfectly clear and utterly transparent, but it's actually blue. The blue color of the water in the oceans (and not the blue of the sky) is the reason why Earth is mostly blue as seen from space.

Pure water absorbs some of the light that passes through it. It absorbs red light more than yellow, yellow more than green, and green more than blue. Only the deepest blue light can travel very far through water, so a large mass of water takes on a deep blue color.

The blueness of water is easily visible in a swimming pool lined with white concrete. It's even visible in a white porcelain bathtub. But the bluest water of all is the clear tropical ocean far from land, where the sea is much bluer than the sky.

The color of the ocean is strongly affected by plankton and impurities: Reference 1 - Reference 2

More Cool Facts about water: Reference 1 - Reference 2 - Reference 3

Will the milky Way Galaxy collide with another galaxy?
According to astronomers, our Milky Way Galaxy has gotten as large as it is by attracting and absorbing smaller galaxies. But our galaxy's history is not yet over and there is a much more dramatic event in the future: a large-scale galactic collision is coming.

There's no need for alarm, though. The collision won't happen for three billion years. The other galaxy is Andromeda, a large spiral much like the Milky Way that is currently almost three million light years away in the northern sky. It is approaching at about 300,000 miles per hour (480,000 km/hour).

When the collision happens, the two galaxies will probably merge into a single large elliptical galaxy. But the sun will most likely survive just fine, since stars in a galaxy are so far apart that they seldom collide during galactic collisions.

Andromeda is the nearest large galaxy to our own: Reference 1 - Reference 2 - Reference 3

What happens when galaxies collide: Reference 1

What are the conditions at the center of the Earth?
Even the deepest boreholes have not yet penetrated the thin outer crust of the Earth. Yet scientists have been able to determine some properties of the core from their understanding of planet formation, and from the behavior of seismic waves (waves generated by earthquakes) as they move through the Earth.

The two most significant properties of Earth's core are temperature and pressure. The temperature is nearly 7,000 Kelvins (12,000 F). At that temperature, hotter than the surface of the sun, all matter radiates a blinding white light.

The pressure at Earth's core is millions of times new roman that at the surface. Under such great pressure, the iron-nickel mixture there has solidified into a solid sphere 1,500 miles (2,400 km) across, which floats in the center of a sea of white-hot liquid metal.

More about the Earth's core: Reference 1

The reasoning behind our current understanding of the core: Reference 1

What it's like at the center of the sun: Reference 1

Where is the greatest diversity of fruit flies?
Of all locations where fruit flies (Drosophila) are known to live, the largest number of species in one place is in the Hawaiian islands. There are more than 1,000 different kinds there, about 25% of all species worldwide.

Ecologists believe Hawaii has so many kinds of fruit flies because the islands were isolated for millions of years. When the first fruit flies arrived, they were able to evolve quickly because there were few competing species of flies. For the same reason, when people first arrived at the islands centuries ago, they found that there were thousands of unique species of birds, plants, and other life forms.

However, people have over time brought many new species with them to the islands, and the competition is driving most of the native species into extinction. Even the unique Hawaiian fruit flies are disappearing, replaced by flies from other parts of the world.

How fruit flies get into your kitchen, and what they actually eat: Reference 1

Crickets and fruit flies in Hawaii: Reference 1

An essay on speciation: Reference 1

Why flies are so good at flying: Reference 1

What are the smartest dogs?
While it can be tricky to measure the intelligence of a dog, there is general agreement among dog fanciers that the smartest dogs are the border collies. These versatile, playful, athletic dogs were originally bred for herding sheep on farms. They are able to learn and carry out complex tasks requiring several hours of focused effort.

While most breeds of dogs are bred for physical appearance, border collies are bred for all-around general intelligence and robust good health. Border collies are not usually entered at dog shows and most do not carry professional papers, but their breeders are no less passionate than those of other breeds.

Because of their great intelligence and energy, border collies do not necessarily make ideal pets. They require a lot of stimulation and if left alone may get into trouble, especially in a non-rural environment.

Stories and information about border collies: Reference 1

Reference 1

More Cool Facts about dogs: Reference 1 - Reference 2 - Reference 3

How many times do our eyes move in one day?
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: Reference 1

An experiment to see the retina of your own eye: Reference 1

The smallest eye movements are called saccades: Reference 1

More Cool Facts about eyes: Reference 1 - Reference 2

What was the largest landslide in recorded history?
Although the eruption of Mount St. Helens on May 18, 1980 was far from the largest volcanic explosion ever recorded, it triggered the largest landslide in history. By the time the eruption was over, there were 230 square miles (600 square kilometers) of fresh wasteland below the volcano, including mounds of landslide debris as tall as 240 feet (73 meters).

The eruption blew off the top 1,300 feet (400 m) of the mountain, and the landslide scoured a giant gash that turned the classically-shaped conical volcano into a rough, cratered mound with a large gap in one side. The entire north face of the mountain gave way, and the ensuing landslide raced as far as 15 miles downslope (24 km). Avalanche-related mudflows extended as far as the Columbia River, 48 miles away (77 km).

Since the eruption, life has returned to Mount St. Helens. The landslide debris is now covered by a young, healthy ecosystem of forests and meadows.

Mount St. Helens National Volcanic Monument: Reference 1 - Reference 2

See how Mount St. Helens looks right now with this live webcam: Reference 1

The largest known volcanic explosion on Earth: Reference 1

How do hunting spiders find their way home?
Some kinds of spiders use the polarized light of the sky as a compass to find their way back to their nests. These spiders, who are active hunters at dusk and dawn, sense the light's polarization with a pair of special eyes.

The two direction-finding eyes are on the top of the spider's head, right behind its primary image-forming eyes, which are much larger. Each iridescent blue directional eye has a V-shaped crystal that only allows light through that is polarized in a particular direction. The two eyes have crystals whose polarizations are at right angles to each other. Because of their special construction, they can't form images.

In a study, spiders whose directional eyes were covered had trouble finding their way back to their nests. Since the sky's polarization is greatest right around dawn and sunset, it makes sense that these twilight-active hunting spiders would use polarized light as a directional clue.

More about the spider's compass eyes: Reference 1 - Reference 2

Jumping spiders have the most acute vision: Reference 1

What is the only magnetic moon in the Solar System?
The largest planetary satellite in the Solar System is also the only moon known to have a substantial magnetic field. When the Galileo spacecraft first approached Jupiter's moon Ganymede, it recorded bursts of radio noise and magnetism that revealed a teardrop-shaped magnetosphere, just like Jupiter's.

Ganymede's magnetic field is embedded in the much vaster magnetic field of Jupiter, which in turn is embedded in the enormous magnetic bubble carved by the Sun from the galactic field. Earth's magnetic field is embedded in the same bubble.

It is not clear how Ganymede can generate a magnetic field. To do so, it must contain an inner core or layer that conducts electricity. Is its core made of metal? Is there a layer of salty water above the core? Future exploratory missions may help settle the mystery.

Galileo's Ganymede flybys made exciting discoveries: Reference 1

More about Ganymede: Reference 1

Ganymede is the largest moon in the Solar System: Reference 1

What's the longest river in the world?
Measuring 4,132 miles (6,650 km), Africa's Nile River is the world's longest. It runs from two main sources, one in the Ethiopian highlands (the Blue Nile) and the other from Lake Victoria (the White Nile) north across the Eastern Sahara Desert, emptying into the Mediterranean Sea. The most distant source is the Kagera River in Burundi.

The Nile played a vital role in the earliest history of humanity. It was one of the first rivers whose banks and floodplains were cultivated, and its annual floods were important to ancient Egyptian civilization.

One of the Nile's unusual features is that it is in flood phase when the northern desert is in its hottest, driest season. Fed by torrential rains in the southern mountains, these summer floods were a mystery to European explorers.

Map of the Nile basin:
Reference 1

More about the Nile: Reference 1 - Reference 2

The world's muddiest river: Reference 1

What land animals had the largest skulls?
Of all the animals that ever walked on land, those with the largest skulls of all were the Torosaurus. These ceratopsians (horned dinosaurs) lived between 65 and 70 million years ago during the late Cretaceous Period in what is now North America.

Measuring up to nine feet (three meters) long, the skull of a Torosaurus had a thin, bony frill with two holes. They were also decorated with two large horns over the eyes, a third horn at the tip of the narrow snout, and a pointed beak. The entire animal was up to 24 feet (7.5 meters) long, and weighed up to five tons.

Little is known about Torosaurus; only 21 specimens have been identified, and there are no complete skeletons so far. From the shape of the skull and beak, it seems that they lived in herds and ate plants, as did the better known herbivorous dinosaurs like Triceratops. It is believed that the beak was adapted for tearing up very tough vegetation.

More about Torosaurus: Reference 1 - Reference 2 - Reference 3

The first mostly-complete dinosaur skeleton: Reference 1

Has Niagara Falls ever been dry?
According to recent research, the first trickle of water dripped off the cliffs of Niagara about 12,000 years ago as the glaciers of the last Ice Age began to melt. But the Falls in those days were only about one-tenth of their current size, and before they would grow they actually vanished for a while.

The reason is related to the disappearance of the glaciers: as the ice melted and removed its great weight from the landscape, the Earth's surface tilted and caused the glacial meltwater to flow north for a while. But as the last of the ice melted, the landscape began tilting back.

Some time before about 5,000 years ago, the Falls returned and quickly built to their present volume of more than 500 million cubic meters per day (5.4 billion cubic feet).

The origin and history of Niagara Falls: Reference 1

Niagara Falls facts: Reference 1

An ice jam upriver caused the flow over Niagara to come to a halt: Reference 1

What US state is most densely forested?
Of all the states, Maine has the largest ratio of forest to non-forest land. 89.8% of that state is classified as "wooded" by the US Forest Service. Next is New Hampshire at 88.1%, followed by West Virginia at 77.5%.

More than 3.5 million acres of Maine's forests are contained within a sprawling region called the North Maine Woods. The crown jewel of the area is the protected Allagash Wilderness Waterway, a national treasure that includes more than 2.5 million acres of pristine forest.

While not technically a wilderness area, the North Maine Woods is almost entirely rural. It is mostly privately owned, and there is a strong, coordinated effort by its landowners to restrict development in order to preserve the land's natural beauty and diverse ecosystems.

More about the North Maine Woods: Reference 1

Threats to the North Maine Woods continue: Reference 1

Some feel the area should be made into a National Park: Reference 1

When is the Earth closest to the Sun?
You might think that the Earth is closest to the Sun when the weather is warmest, but that's only true south of the equator. Earth's closest approach to the Sun (perihelion) happens around January 2, when it's winter in the north.

Earth's orbit is so close to circular that the difference in distance between the closest and farthest points is very slight. The atmosphere and oceans hold so much of the Sun's warmth, that the effect of the distance changes is mostly invisible.

On a longer time scale the effect may be much more important. The time of perihelion shifts by 25 minutes each year, making a full cycle around the yearly calendar every 21,000 years. This (and other long-term cycles) may be part of the reason for the ice ages.

The Sun at perihelion in 2000: Reference 1

The 21,000 year Milankovitch cycle: Reference 1

How does the Earth lose water?
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!): Reference 1

The Polar spacecraft measures the "auroral fountain" of ions: Reference 1

Cool Facts about auroras, also produced by streams of charged particles: Reference 1 - Reference 2 - Reference 3

What planet's surface has the most extreme climate?
Of all the planets in the solar system, the one with the greatest surface temperature variation is Mercury, the closest to the sun. During the day, its surface temperature gets up to 400 Celsius (752 F) beneath a sun that appears much larger than it does from Earth, while at night the temperature is a chilly -200 C (-328 F).

Still, Mercury is not the hottest planet. Even though Venus is further from the sun, its surface temperature is a searing 470 C (878 F), which is hot enough to melt lead. Venus is hotter because its atmosphere traps the sun's heat in a runaway greenhouse effect. Vnus' thick atmosphere also keeps the surface temperature very steady, unlike Mercury, which has almost no atmosphere.

In addition to the planets, there are some comets that have even more extreme surface temperature variations as they swing in close to the sun, then back out into deep space. Most of these "sun grazers" don't last very long because they are vaporized during close solar flybys.

Mercury is a mysterious little planet: Reference 1

There are planets in orbit around other stars as well: Reference 1

What kind of spider steals food from other spiders?
If you look closely at the web of a giant golden orb spider (Nephila edulis), you might see much smaller spiders on it. These round, silvery nest parasites are droplet spiders (Argyrodes antipodianus) waiting for small prey that their giant host ignores.

Small prey insects are not the droplet spiders' only food. These crafty little thieves sometimes band together and carefully steal large prey that the host spider has caught and wrapped, but not yet eaten.

One by one, they cut the lines between the catch and the main web, carefully repairing damage by bridging the gap with their own webs. Then they carry the prey off to a corner, where they can safely consume it.

Pictures of Nephila and droplet spiders: Reference 1

A spider enthusiast's observations of spiders, including Nephila: Reference 1

More Cool Facts about spiders: Reference 1 - Reference 2 - Reference 3

Why is there no "Q" or "Z" on many telephones?
The telephone's pad of twelve buttons reflects its history. There are three letters on most buttons, except for zero, one, octothorp (#) and the star symbol (*), which have no letters. "Q" and "Z" are usually missing from the list. Why?

Instead of twelve buttons, telephones used to have circular plates with ten holes numbered from zero to nine. To make phone numbers easier to remember, the phone companies assigned letters to the numbers, so people could remember mnemonics like "Charleston" for C-H instead of the first two digits of a number.

Of the ten digits, zero was already used to dial the operator and one was used for internal phone company signals. That left eight numbers to which letters could be assigned. Three letters per number took care of 24 of the alphabet's 26 letters, and the least common letters "Q" and "Z" were left out, but not forever. Many telephones now show "Q" on the seven button, and "Z" on the nine button.

Early work on dial telephone systems: Reference 1

The history of the telephone: Reference 1

Why does a week have seven days?
No one knows exactly where and when the seven day week got started, but it is known to be extremely ancient. The most common theory about its origin relates the seven days to the ancient astrological idea that there were seven celestial bodies revolving around the stationary Earth.

For thousands of years, the astrological seven day week was used in Mesopotamia. It was adopted by the Egyptians, who then passed it on to the Greeks. In 321 AD, Constantine The Great added the seven day week to the Roman calendar, making the first day a day of rest and worship.

What were the days of the Roman week? They were Dies Solis (Sun's Day), Dies Lunae (Moon's Day), Dies Martis (Mars's Day), Dies Mercurii (Mercury's Day), Dies Iovis (Jupiter's Day), Dies Veneris (Venus's Day), and Dies Saturni (Saturn's Day).

Starting next Monday, Learning Kingdom's Cool Word Of The Day will take a tour of the English names for the seven days of the week.

More about the days of the week: Reference 1

How many active languages are there in the world?
According to recent estimates, the number of actively spoken languages in the world today is around 6,000. More than 1,400 of those languages belong to the Niger-Congo family from Africa, and about 1,200 are in the Austronesian family from Madagascar, Indonesia, Australia, the Pacific Islands, and New Zealand.

Most of today's active languages are spoken by very few people, and many of them are losing speakers rapidly as the world becomes more and more connected. Half of today's languages have fewer than 10,000 speakers, and a quarter have fewer than 1,000.

Thousands of years ago, there may have been as many as 10,000 active languages in the world. Within the next century, thousands of languages may be lost.

More about the disappearing languages of the world: Reference 1

A directory for sites about native languages around the world: Reference 1

More Cool Facts about languages: Reference 1 - Reference 2

What's the fastest that humans have ever traveled?
Relative to the planet Earth, the fastest speed humans have achieved was 24,791 miles per hour (39,914 km/hr), by the Apollo 10 astronauts, on their return trip from the moon in 1969.

But the universe is much bigger than the Earth-Moon system, and everything moves. If the Sun is taken as a fixed point, then all the humans on Earth are moving at about 66,660 miles per hour (107,320 km/hr) as the Earth follows its orbit.

If the center of the Milky Way galaxy is a fixed point, then the solar system is moving at about 500,000 miles per hour (800,000 km/hr) in its orbit around the galaxy.

From an even broader reference frame, our entire local group of galaxies is moving at about one million miles per hour toward another galaxy group called Virgo Cluster.

Apollo 10 did not include a moon landing, but it did include the first live color-TV from space: Reference 1

Virgo Cluster contains about 2,000 galaxies: Reference 1

A Cool Fact about the fastest human-made object: Reference 1

A Cool Fact about Earth's orbit around the Galaxy: Reference 1

How can a cricket be used as a thermometer?
If you hear a cricket chirping and you have a watch, you can estimate the temperature where the cricket is. If you can hear more than one, you can tell whether they are experiencing different temperatures.

To calculate the "cricket temperature," count the number of chirps in a 14-second period. Add forty to the result, and you have a rough estimate of the Fahrenheit temperature of the cricket.

This method works best with the snowy tree cricket, whose song sounds like gently ringing sleigh bells. Depending on the species of cricket, you might have to adjust the counting time by one or two seconds, up or down.

Why does it work? Because crickets are cold-blooded creatures, the rate of their metabolism is strictly determined by temperature. The warmer it is, the faster they move and the faster they chirp. The same method would work equally well with other insects if they had the regular chirping habits of crickets.

Scroll down this page to read about crickets: Reference 1

Crickets and their relatives, grasshoppers and katydids: Reference 1

Another Cool Fact about crickets: Reference 1

What is a sonic boom?
Sonic booms are not often heard these days in most inhabited parts of the world. That's because they can be somewhat destructive, not to mention annoying. They are caused by aircraft that travel faster than the speed of sound.

The sonic boom is a shock wave that forms when the aircraft's speed outstrips the ability of air molecules to get out of the way. It's a moving pressure wave that starts at the nose, wingtips, and other forward-projecting parts of the aircraft and forms a cone trailing back from the plane and expanding up, down, and out to the sides.

When that cone-shaped pressure field passes across a point on the ground, a sonic boom is heard. Since the pressure wave of a moderate sonic boom can be enough to break windows, non-military aircraft are no longer allowed to travel faster than sound near inhabited areas.

More about sonic booms: Reference 1 - Reference 2

Sometimes a large meteor causes a sonic boom: Reference 1

More Cool Facts about sound: Reference 1 - Reference 2 - Reference 3

What was the best throwing weapon before bows?
Before the bow and arrow were invented about 15,000 years ago, a simpler weapon was used to throw long darts with great power and accuracy. The atlatl [at-LAT-ul] was invented at least 25,000 years ago, and is still used by Australian aborigines.

The atlatl is a stick about 60 centimeters long (24 inches), with a notched hook at one end. Into the notch is placed the end of a flexible, feathered "dart" that is at least 150 centimeters long (59 inches) and possibly longer. By flicking the atlatl quickly forward, the user is able to fling the dart toward the target with tremendous speed.

Recently, there has been a surge of interest in the atlatl. Its physics are surprisingly sophisticated, involving temporary storage of energy in the flexing of the dart as it is thrown. Enthusiasts are now designing ever-better atlatls using high-tech materials, and there are world-wide competitions.

The World Atlatl Society: Reference 1

World Atlatl Magazine: Reference 1

More Cool Facts about weapons: Reference 1 - Reference 2 - Reference 3

What's the oldest brand of carbonated drink?
The oldest commercially marketed carbonated drink is Moxie, which became available in apothecaries as a medical tonic in 1876. Made by the Nerve Food Company of Lowell, Massachusetts, Moxie was first sold as a beverage in 1884. (Hires Root Beer was also introduced in 1876.)

Moxie has an odd flavor that has been described as a combination of cola, root beer, and licorice. The first version contained wintergreen as well as a bitter-sweet herb, root gentian. According to those who like it, it is definitely an acquired taste.

Moxie was also the first carbonated beverage to offer a sugar-free version. The potent brew with its distinctive orange labels is still available in Maine, where it is something of a local classic.

Moxie is one of the favorite drinks at Bates College in Lewiston, Maine: Reference 1

Go to Lisbon Falls, Maine and experience Moxie Days: Reference 1

Today's Cool Word is moxie: Reference 1

Why did the Tower Of Pisa tilt to one side?
On August 9, 1173, construction began of a beautiful new bell tower at Campo dei Miracoli (Field of Miracles), Pisa, Italy. By the time the first meter and a half (five feet) of the base was complete, it was clear that it was tilting.

Over the next two centuries, construction was halted and restarted several times. The upper floors of the tower were built askew, in an attempt to adjust for the tilt. As a result, the tower bends upward, as if trying to overcome gravity.

The tower's tilt was caused by uneven sinking of its foundation into sandy, marshy soil. It continued to lean further every year, until recent excavations and reinforcements were made. Work continues to ensure that the beloved Leaning Tower will never fall.

More about the Leaning Tower of Pisa: Reference 1

More Cool Facts about tall buildings: Reference 1 - Reference 2 - Reference 3

How did "qwerty" keyboards become standard?
Almost every alphabetic keyboard in the world has the letters in an arrangement called "qwerty," after the first six letters in the top row. There are several popular myths about the origin of today's standard keyboard arrangement. Some say it was deliberately designed to slow down typists. What is the truth?

When inventor C. L. Sholes built his first typewriters in 1868, he arranged the keys in alphabetical order. But the clumsy mechanical linkages inside the machine could tangle if certain pairs of keys were struck quickly.

The "qwerty" arrangement fixed the tangling problem by separating the internal links for frequently paired letters, making the machines more reliable. After a historic typing contest (see today's Person Of The Day, linked below), "qwerty" became the standard way to arrange the keys.

More about the real history of the "qwerty" keyboard: Reference 1

Reason Magazine article about market myths, including the origins of "qwerty" and its most popular modern competitor, the Dvorak keyboard arrangement: Reference 1

Today's Person Of The Day was the first person to master touch typing: Reference 1

Why will New Orleans will soon disapear?
For millions of years, the Mississippi River ran freely across its delta into the Gulf of Mexico, flooding every year and building up layer upon layer of sediments. Each year, the sediments sank under their own weight and the floods added more layers on top.

Then humans came and built a city that they called New Orleans. Unfortunately, they also penned the waters of the river into narrow channels. The floods no longer added new layers, and the land beganto sink.

Today, most of New Orleans is sinking at a rate of three feet (1 meter) per century, and on average the whole city is already eight feet below sea level (2.4 meters). Rising sea levels caused by global warming make the problem even worse. Although efforts are under way to protect the city, it is likely that large parts of New Orleans will be underwater within decades.

News stories about the growing problem: Reference 1 - Reference 2

Introducing New Orleans, its history and features: Reference 1

What kind of fax machine makes 3-Dimensional objects?
A normal fax machine receives a coded message over the phone and translates it into a pattern of black and white dots on a page of paper. But there's a kind of fax machine that builds a three-dimensional object instead of a picture on paper.

Charles Hull invented the process, called stereolithography or solid imaging, in 1984. More than just a 3-D fax machine, it's a whole new way of making things. Descriptions of objects are stored as computer data files, which can be given physical form in a solid imaging machine.

A solid imaging machine creates an object by scanning a light beam across the surface of a liquid. The liquid solidifies wherever the light touches it. The newly created solid is lowered slightly, and another scan adds another layer of solid material. An object of almost any shape can be created.

More about stereolithography: Reference 1 - Reference 2

Description and diagram of a solid imaging machine: Reference 1

Why is it so important? Reference 1

What's the hottest kind of flame?
The hottest flames known to science are made by burning a mixture of oxygen and acetylene (C2H2). The flame of an oxyacetylene torch can reach a temperature of more than 3300 degrees Celsius (5972 F), hot enough to melt metal even underwater or in the extreme cold of Antarctica.

Why does acetylene produce such a hot flame? The secret is in the molecule's structure: It contains two carbon atoms joined by a high-energy triple bond, with a hydrogen atom capping each end of the molecule. When the triple bond is attacked and broken by oxygen atoms, a very large amount of energy is released.

Because of its extremely high energy content, acetylene is also one of the most explosive gasses. Even a small amount, if it explodes, can create a shock wave intense enough to kill a person and flames hot enough to inflict severe burns.

A prize-winning essay about acetylene: Reference 1

How dangerous is it? Reference 1

More Cool Facts about fire: Reference 1 - Reference 2 - Reference 3 - Reference 4

Where are spider webs used as fishing nets?
Natives of New Guinea, a lush tropical island north of Australia, use the webs of giant Nephila orb spiders as fishing nets. The spiders that make these webs are among the largest arachnids in the world, able to trap and eat small birds. Their bite is very painful, but usually does not kill.

Fishermen in Polynesia use the webs of a closely related spider as fishing line. Their golden orb weaver fishing lines can haul in single catches big enough to feed several people.

The webs of Nephila spiders are beautiful marvels of natural design. Cast across human-size or larger gaps, they form a slightly tilted bull's eye, often with a vertical design made out of the remains of prey.

More about Nephila spiders: Reference 1

A golden orb weaver and its web: Reference 1

Another bird-eating spider: Reference 1

How do forest workers in Bengal protect against tigers?
The mangrove forests of the Sunderbans in West Bengal, India are home to deadly Bengal tigers, which are easily able to kill a human. Yet hunters, woodcutters, and honey gatherers often enter these swampy forests. How do they protect themselves?

Each person who enters the Sunderbans wears a rubber mask of a human face on the back of his or her head. The belief is that the tiger will only attack its prey from behind. If it can see your face, it will not attack.

The masks, issued by the government, are part of a larger program that includes the placement of electrified human dummies and the construction of freshwater ponds to keep the tigers out of the rivers, where people are often attacked.

The Sunderbans is one of the few places where the tiger population is growing: Reference 1

More about the highly endangered Bengal tiger: Reference 1 - Reference 2

A reptilian tiger-equivalent that lived 260 million years ago: Reference 1

How long was an hour in ancient times?
The ancient Greeks, Romans, and Egyptians divided the day into 24 hours, but their hours were not all the same length.

The day was divided into ten hours of light, two hours of twilight, and twelve hours of darkness. The timing of the hours in a given day depended on the position of the sun, so the hours' lengths changed with the seasons. It was not until the invention of mechanical clocks in the late Middle Ages that the hours were set to identical lengths.

Most of the earliest clocks used a moving shadow to indicate the passage of time. As early as 3500 BC, there were tall, thin stone obelisks whose shadows crossed the surface of a flat plaza over the course of the day. Those, and later sundials, were marked with varying scales of hours for the different seasons. A related device called the Merkhet was developed in Egypt around 600 BC to tell time at night by measuring the movements of stars.

The first clocks: Reference 1

The first clocks with hands: Reference 1

The most accurate clocks: Reference 1

How do spacewalking astronauts stay warm (or cool)?
The environment of space is one of the most punishing that humans have ever entered. In sunlight the temperature can rise to 120 degrees Celsius (250 F), while in the shade it can get as cold as-150 Celsius (-250 F).

To keep their human occupants comfortable, modern space suits are marvels of high-tech design. The astronaut's entire body is surrounded by 90 meters of water-filled plastic tubing (295 feet). The water circulates through a device in the suit's backpack called a sublimator, where heat is removed by evaporating some of the water.

Since the sunny side of the astronaut is so much warmer than the shadow side, the water tube layer is surrounded by a layer of insulating aluminized mylar, along with several other layers designed to hold in the pressure of the suit's pure oxygen atmosphere and to protect against the impact of micrometeoroids.

More about space suit design: Reference 1

Reference 2 - Reference 3 - How the cooling technology of space suits helps MS victims: Reference 1

A new kind of robot will fly with astronauts soon: Reference 1

What kind of cloth was made from part of a shellfish?
Divers in the Mediterranean Sea used to collect gold-colored strands from a mollusc called the noble pen shell, amber pen shell, or fan mussel (Pinna carnea or Pinna nobilis). These fibers, or byssus, are used by the pen shell animal to secure itself to rocks and other objects.

Until the Middle Ages these fibers were used to weave a strong but supple fabric called "cloth of gold." This cloth was so fine that a pair of ladies' gloves made from it could be folded and packed inside a walnut shell.

The art of making cloth of gold has been lost to time, and the pen shell is now much less common. But there are still a few examples of the cloth in museums, and the fabric is still soft and golden.

How shellfish have been used throughout history:">Reference 1

Picture of the noble pen shell: Reference 1

A marine mollusc that eats wood: Reference 1

What was the first official U.S. coin?
The first U.S. coin was the Fugio copper penny. It was minted in 1787 to help deal with the problem of underweight or counterfeit copper pennies circulating at the time. By minting a national coin, a standard could be established.

The coins bore a sun and sundial on the front, with the inscription "FUGIO" (I fly) and "MIND YOUR BUSINESS." On the back were thirteen linked rings with the words "WE ARE ONE" and "UNITED STATES." Benjamin Franklin designed the coin.

Unfortunately, the Fugio cent had a troubled birth. The contractor who had agreed to press the coins used much of the copper for another coinage, and eventually fled to Europe to avoid prosecution by the U.S. government. Only a few thousand Fugios were ever made, and it is uncertain if any were ever put into circulation.

Images and descriptions of some Fugio cents: Reference 1

The story of the Fugio cents: Reference 1

Why some coins have notches around the rim: Reference 1

What's the most powerful chemical explosive?
Until recently, the most powerful known chemical explosive was a substance called octogen, a military explosive. But now there's a serious challenger on the scene. Called octanitrocubane (ONC), it's the most energy-dense explosive known, and could be as much as 25% more powerful than octogen and twice as powerful as trinitrotoluene (TNT).

ONC is a powerful explosive for two reasons: first, it is very dense, almost twice as dense as water. Because of its density, it releases a large amount of energy in a small volume.

The second reason for its explosive power is in its molecular structure. A highly strained cube of eight carbon atoms is adorned by eight energy-rich nitrate (NO2) groups. When it burns, ONC almost instantly turns into a very hot gas of nitrogen and carbon dioxide.

Octanitrocubane was recently synthesized for the first time: Reference 1

Cubane, the base molecule of ONC, is a very strange substance: Reference 2

Why large explosions create mushroom clouds: Can electronic devices be made out of plastic?
Although most kinds of plastic do not conduct electricity, there are some that do. These special plastics, which have alternating double and single bonds in their molecules, are now being used to make integrated circuits without using any metal at all.

Although circuits and chips made out of plastic are slower and larger than their silicon cousins, they are also cheaper and show promise of being easier to make. Some kinds of plastic circuits might even be sprayed onto surfaces by machines much like ink-jet printers.

Some plastic electronics can be bent and twisted while still functioning. Some are waterproof, and some are so cheap they can be made by the thousands and used disposably. They are already being used for security tags at stores, and many more applications are coming.

Making electronics out of plastic and other organic materials: Reference 1 - Reference 2 - Reference 3

The smallest graffiti in the world is on computer chips: Reference 1

What is the secret of radar-absorbing paint?
Military vehicles can benefit from being invisible to enemy radar. Special paints and other coatings have been developed to absorb radar signals without reflecting them back. Most of these coatings include particles of conductive substances in a matrix of non-conducting binder.

The special paint used on the SR-71 Blackbird jet, for example, contains thousands of tiny glass spheres coated with a magnetic layer of metal ferrite. The spheres absorb radar waves and turn them into heat before they can be reflected. Another kind of radar absorber called Halpern Anti-Radiation Paint includes tiny metal flakes aligned in opposite directions in successive layers.

No material is a perfect absorber, but when high quality "stealth paint" is applied to a properly shaped vehicle, its radar cross section can be dramatically reduced. The B-2 Spirit bomber, for example, with a wingspan of 52 meters (171 feet) looks no bigger than a bird on a radar scope.

More about stealth technology in military vehicles: Reference 1

The B-2 is a marvel of stealth technology: Reference 1 - Reference 2

Technical article about various stealth coatings: Reference 1

Who invented rockets?
The ancient Chinese, who also invented gunpowder, used the first rockets in war. To make "fire arrows" they tied bamboo tubes filled with gunpowder to ordinary arrows. The "Wu-ching Tsung-yao" (Complete Compendium of Military Classics), written in 1045, describes such weapons.

Rocketry evolved further in succeeding centuries leading to much more effective weapons and also to projectiles similar to modern fireworks. Innovations included exploding shrapnel bombs, cannons, and arrays of up to 1,000 fire arrows that could be triggered all at once.

Faced with Chinese rockets, the Mongols came up with their own versions in one of history's first technological arms races. Later, Europeans developed their own rockets and invented many other uses of gunpowder.

More about the first rockets: Reference 1

Chinese rocketry led to today's Chinese space program: Reference 1

The smallest rockets: Reference 1

What was the first known use of the wheel?
The first wheels were not part of moving vehicles. They were potter's wheels, probably invented around 6500 BC by artisans in Asia Minor. The first known wheeled vehicles were not in use until 3,000 years later, in 3500 BC in Sumer and Syria.

The first potter's wheels were quite simple. A flat, stone disk was mounted horizontally on a pivot and spun, with wet clay at the center of the disk. Since both of the potter's hands were occupied with shaping the clay, an assistant was needed to keep the wheel spinning. Later designs included a stick that was inserted into a notch to turn the wheel.

A major improvement came in 16th century Europe, when a separate flywheel provided much better speed control. The foot treadle, invented in the 19th century, was a further refinement, followed by variable-speed electric motors.

The history of pottery around the world: Reference 1

Pottery was already a very old technology in 6500 BC: Reference 1

Where is the world's largest airport?
You might think that the world's largest airport would be near one of the world's largest cities. Actually, the largest airport in the world (measured by total land area) is Saudi Arabia's King Khalid International Airport, which covers 87 square miles (225 square km). Located near Saudi Arabia's capitol, Riyadh, it was opened in 1983 and like Riyadh it is surrounded by hundreds of miles of empty desert.

When it was first opened, King Khalid Airport (air traffic code: RUH) had the capacity to handle 7.5 million passengers a year. Projections then claimed that by the year 2000 that capacity would be doubled. It is one of the most modern airports in the Middle East, with a high-tech industrial park nearby that specializes in the aviation industry.

What Saudi Arabia says about the airport: Reference 1

Basic facts about Saudi Arabia: Reference 1

A guide to the world's airports: Reference 1

How does the Global Positioning System work?
One of the wonders of the modern world is that a handheld electronic instrument can tell you exactly where you are on the planet, including your altitude. This is the Global Positioning System (GPS), which uses a fleet of 24 satellites carrying extremely accurate clocks to aid navigation worldwide.

When a GPS receiver is activated, it listens on radio frequencies for signals from the GPS satellites. These signals contain precise information about each satellite's location in space, along with the exact time when that information was sent out.

When the receiver has time and location information from four different satellites, it uses its own computer to figure out where you are. By taking into account how long each signal took to travel at the speed of light and exactly when it arrived, the GPS unit can determine where you are.

A GPS primer for students: Reference 1

Atomic clocks make GPS possible: Reference 1

Technical description of the GPS system: Reference 1

Cool Facts about atomic clocks: Reference 1 - Reference 2

How did a map help stop an outbreak of cholera?
In London in the 1830s through the 1850s cholera was a major disease, often reaching epidemic proportions. Preventing these epidemics was almost impossible without our modern understanding of how diseases are transmitted.

It was not until 1854 that a real breakthrough came. A doctor named John Snow carefully mapped the location of each case. He discovered that one particular outbreak was clearly centered around a single water pump in a certain section of town.

He advised local officials to remove the handle of that one water pump, and before long the outbreak ended. He had proved his theory that the cholera was being transmitted, at least in part, through the public water supply.

How John Snow made a great leap for epidemiology: Reference 1

John Snow is today's Person Of The Day: Reference 1

What kind of car flies through the air?
In the 1930s a small winged automobile called the aeromobile was designed, and one was actually built. The aeromobile could fly through the air, but its performance, both on the ground and aloft, was not spectacular.

Now a new kind of flying car has been created that not only takes off vertically, but could also be the commuter vehicle of the future. Paul Moller's Skycar uses eight turbo engines to fly easily at 350 miles per hour (564 kph) using ordinary gasoline.

The Skycar is a new class of vehicle (called a volantor by Moller) that might make personal air transportation easier and safer than a ground trip. It could be equipped with a sophisticated computer autopilot that could safely fly its occupants to any destination, without human intervention.

Moller International's page on the Skycar: Reference 1

Article about the Skycar: Reference 1

More Cool Facts about innovations in air travel: Reference 1 - Reference 2 - Reference 3

What kind of material has no electrical resistance?
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: Reference 1

More Cool Facts about electricity: Reference 1 - Reference 2 - Reference 3

What was the first animal sent into space?
The first animal in space was carried into orbit in the second artificial satellite, Sputnik 2. She was the dog Laika (Barker), launched from the Baikonur Cosmodrome by the Soviets on November 3, 1957.

The capsule's primitive life support system kept Laika alive until the oxygen ran out a few days later. On April 14, 1958 Sputnik 2 fell into the atmosphere and burned up.

The Soviet Sputnik program sent more than a dozen dogs into space. The last Sputnik dog was Chernushka (Blackie), whose successful flight in March, 1961 preceded Yuri Gagarin's manned orbital flight the following month.

The history of dogs in space: Reference 1

A Cool Fact about Sputnik 1: Reference 1

How are large buildings protected against earthquakes?
If a large building is firmly attached to the ground, an earthquake can rip it right off the foundation. Making a building more solid can solve the problem for some quakes, but it's an expensive solution that only works for moderate quakes. There's a better way to protect large buildings.

Base-isolated buildings can survive even large earthquakes because the building itself is not firmly attached to the ground. When the shaking starts, the building stays relatively still while the ground moves underneath.

There are several ways to base-isolate a building. Rubber pads can be inserted between the building and the foundation, or it can rest on sliding or swinging bearings that move back and forth easily. Such a system protects the largest base-isolated building in the world, a new terminal at San Francisco International Airport.

Advanced ways to protect against earthquakes: Reference 1

Base-isolated buildings in Japan: Reference 1

SFO's new International Terminal: Reference 1

North America's largest recorded earthquakes: Reference 1

What's the oldest printed book with a date?
The oldest known printed book that can be clearly dated is a copy of the Sanskrit Vajracchedika-prajnaparamitasutra (Buddha's Diamond Sutra), dated by its maker on May 11, 868 AD in China. It is one of Buddhism's greatest treasures.

To make the book, seven rolls of paper were printed with wooden blocks, then cut and glued together. It is written in Chinese, with elaborately detailed illustrations of the Buddha and his disciples.

Although the Diamond Sutra is the oldest dated book, it is not the oldest printed work. Wood block printing was known for more than 100 years prior to the Diamond Sutra's printing.

The original Diamond Sutra is at the British Library Exhibition Galleries: Reference 1

The full text in English, interpreted by a Buddhist monk: Reference 1

The oldest papyrus document ever found: Reference 1

How are construction cranes placed atop new buildings?
Huge steel cranes usually top skyscrapers, and are used to lift construction materials to the top.

These "climbing tower cranes" get to the tops of the buildings by climbing up a steel tower. The steel tower, also called a mast, is built in-place by the crane that climbs it.

At the ground a concrete base is poured and the first section of the tower is bolted deeply into it. The crane cab, arm, and counterweight are installed, along with hydraulic rams that can lift it a little bit at a time. A new tower section is lowered into place by the crane, and then the crane uses the hydraulic rams to move up onto the new tower section. As the building grows, so does the crane tower. When the building is finished, the crane climbs back down, taking the tower apart as it descends.

More about climbing tower cranes: Reference 1 - Reference 2

A robot that can climb tall steel structures: Reference 1

The world's largest construction project: Reference 1

What year was missing ten days in October?
In 1582 Pope Gregory decreed that October's dates would skip from the fourth to the fifteenth, dropping ten days. The reason for this seemingly strange act had to do with the calendar system that was in use at the time.

Unlike our current system, the old Julian calendar had a leap year every four years without exception. Because a year is really a fraction shorter than 365.25 days, tiny errors began to accumulate. By the time of Pope Gregory's decree, the calendar was adjusted by ten days compared to Earth's solar year.

When he issued his decree, Gregory also fixed the leap year rule, so that leap years do not occur on century years (divisible by 100), unless the year is also divisible by 400. There is one other exception: years divisible by 4000 are not leap years. For example, 1900 was not a leap year, but 2000 is one.

More about calendar adjustments and leap years: Reference 1

A suggestion for an even more accurate system: Reference 1

What clock measures time in thousands of years? Reference 1

What's the most accurate clock in the world? Reference 1

When were clock hands invented?
he first known mechanical clocks in Europe were built in the thirteenth century, but they did not have a circular dial or pointers to show the time. These primitive timekeepers had bells or other noisemakers that sounded approximately once every hour.

The first clocks with pointers (hands) were made in the fourteenth century. Those early dial clocks had only one hand, the hour hand. The idea of measuring time more accurately than that was ridiculous in those days, because the clocks were not accurate enough to make it worthwhile.

Although Jost Burgi invented the first clock with a minute hand in 1577, it was not until the invention of the pendulum-regulated clock in 1657 that a minute hand became practical, and second hands were not used until the eighteenth century.

The history of timekeeping: Reference 1

Who invented the pendulum clock? Reference 1

What is the most accurate clock in the world? Reference 1

How are coins designed and produced?
Modern US coins go through a complicated design process, from the first idea to the final product. It starts with an act of Congress to authorize the new coin.

An artist draws a detailed picture of the new design, then a sculptor makes an enlarged, 3-dimensional clay model of the coin. A plaster cast is made of the clay model, and then a rubber mold of the plaster cast. An epoxy coin is cast in the rubber mold, and then a machine engraves a life-size metal proof called a die from the large epoxy cast.

Many of these dies are used in a machine called a coin press, which takes circular pieces of metal called blanks and stamps them with the dies, turning them into actual coins. The coins are checked for flaws, and then released to the banks in counted bags.

More about how coins are made: Reference 1

Reference 1

More Cool Facts about coins: Reference 1

Reference 1

Who made the first marbles?
Marbles have been used for games since the times of the Egyptian Pharaohs, when they were made out of fired clay. Clay marbles were also made by Native Americans, who also used round stones and nuts for their games.

The first glass marbles were made in Venice, Italy around 900 AD. Italian marbles were also made out of polished marble and other kinds of stone around the same time. These stone and glass marbles were used throughout Europe for hundreds of years.

Modern glass marbles did not appear until about 1860, when they were made in Germany. Around 1905, machine-made marbles were first sold in the United States, and their higher quality seriously impacted the European handmade marble marketplace. Today, though, the very best marbles are still made by hand, using secret methods.

More about marble history and collecting: Reference 1

Another Cool Fact about marbles: Reference 1

Marble is a Cool Word: Reference 1

What is the oldest board game in the world?
The oldest board game still played today is Go, a game with only a few very simple rules but such complex strategy that many players dedicate their entire lives to its mastery.

The game is played on a plain grid of black lines, where two players alternate placing black and white "stones" on the intersections, simultaneously trying to capture one another's stones, avoid capture of their own stones, and surround territory.

The aesthetics of the game are as important as the game itself. The best boards are thick, solid pieces of yellow hardwood; the best stones are made from slate and clamshells; the stones are kept in elegant wooden bowls. Although most people play with much less expensive boards and stones, it is possible to spend many thousands of dollars on a nice Go set.

A good introduction to the game: Reference 1

More Go resources: Reference 1

What's the oldest corporate entity in the world?
The world's oldest continuously incorporated company is Canada's Hudson's Bay Company, which was founded in 1670. The company also became the largest corporate landowner with holdings that at one time included about one third of present-day Canada.

During its first two centuries of existence, the Hudson's Bay Company mainly pursued the fur trade, exploration, and settlement of Canada's northern reaches. One of its greatest exploration projects was the unsuccessful attempt to find the fabled "northwest passage" to eastern Asia.

Today, Hudson's Bay Company operates the largest chain of department stores in Canada. It was split into several companies in 1930, so today's Hudson Bay Company is considerably smaller than its illustrious ancestor.

History of the Hudson's Bay Company: Reference 1

During its explorations, HBC accumulated a vast collection of artifacts: Reference 1 - Reference 2

What is the largest construction project in the world?
There has never been a construction project as massive and expensive as China's Three Gorges Dam. This gigantic dam, which will be sixty stories high and 2.3 kilometers long (1.4 miles), will create a reservoir longer than Lake Superior. Scheduled for completion in 2009, the Three Gorges Dam is expected to cost $27 billion and will generate as much electricity as would 18 nuclear power plants.

The massive construction project is also highly controversial, and has generated domestic and international opposition. The reservoir it will create will drown many towns and villages, beautiful valleys, and historic sites. The ecosystem of the Yangtze River downstream of the dam will be permanently changed and some species may become extinct.

A 1998 news story about the dam: Reference 1