Karen Hill

Sometimes a person wandering in a desert may be so thirsty and sun- parched that he begins to see things that aren’t there. This is a hallucination, and not a mirage, for mirages really exist, and can be seen by anyone in the area at the time they appear! A mirage is a trick of … Read more

Each year, thousands of people journey to New Mexico to see Carlsbad Caverns, the largest caverns on earth. These huge underground caves were formed by water dripping from the ground through layers of rock salt and limestone, dissolving the rock and hollowing out the caves. The caverns may be close to five million years old! … Read more

You probably would guess that the Himalayas, which contain 96 of the 109 tallest mountains, is the greatest mountain range on our planet. Actually, the earth’s greatest mountain range is the Atlantic Ridge, which runs north and south under the Atlantic Ocean, from Iceland almost to the Antarctic Circle. This range is 10,000 miles long, … Read more

Lake Huron is one of the Great Lakes, on the border between the United States and Canada. In the Canadian part of the lake, there’s an island called Manitoulin, the largest island in the world that lies within a lake. And on this island is a lake, called Lake Manitou, that might be called a … Read more

Any solid can change to a liquid if it becomes hot enough, and the temperature at which a solid becomes a liquid is called the melting point of that substance. The temperature at which a liquid turns into a gas is called the boiling point. The freezing point of water is 32 degrees F., that’s … Read more

The word “laser” is an acronym, a word formed from the first letters of a series of words. “Laser” actually stands for “light amplification by stimulated emission of radiation.” Invented in the 1950s, the laser is the most powerful source of energy man has discovered. To create a laser beam, light is focused on a … Read more

When it’s 20 degrees centigrade, of course. Twenty degrees centigrade is the same as 68 degrees Fahrenheit, or just about room temperature. Most of the world uses the Centigrade system today, but the Fahrenheit system is much older. This temperature measurement system was named after Gabriel Fahrenheit, a German scientist who was born in 1686. … Read more

Tornadoes have been reported in every state in America, and have occurred in every season! But most tornadoes occur from April to June, and especially strike in the southern states. In recent years, Oklahoma has had the most tornadoes in terms of area: about eight tornadoes for every 10,000 square miles. Mississippi has had the … Read more

Tornadoes, those powerful funnel-shaped windstorms, move along at about 30 miles per hour, carrying winds that may gust up to 200 miles per hour. Most tornadoes follow a path about a quarter- mile wide and 15 miles long, and last less than 20 minutes. But some especially powerful tornadoes move along at more than 40 … Read more

Lightning is caused by electrical charges that build up in the clouds during a thunderstorm, then erupt in a bolt of electricity that reaches between two clouds, or between the clouds and the earth. When a lightning bolt streaks between clouds and the earth, it usually reaches the ground by first striking a tall object, … Read more

The bright flashes of lightning you see streaking across the sky are usually about 300 feet long, but some very powerful bolts may be over five miles long. And lightning bolts can streak to the ground from eight miles in the air, or leap between two clouds 20 miles apart. A lightning bolt may look … Read more

The center of the earth is thought to contain a core of solid iron with a radius of about 850 miles. Surrounding this central core is an outer core of liquid iron, about 1,200 miles thick. And surrounding this outer core is the earth’s mantle, which is about 1,800 miles thick. The crust of the … Read more

Anyone who has been to the Grand Canyon in Arizona would have trouble believing that the awesome gorge isn’t the deepest on earth. True, the Grand Canyon is the largest canyon in the world, over 215 miles long and more than 12 miles across at some points, but the Grand Canyon is “only” about 7,000 … Read more

Icebergs are pieces of ice that break off glaciers or polar ice sheets and drift in the water with ocean currents. Icebergs are being formed continually, and are not rare at all. In fact, they’re so numerous that each year more than a thousand icebergs drift all the way down to the temperate zones. Large … Read more

Antarctica is the continent that surrounds the South Pole. This cold, barren land covers about five million square miles, that’s about 11/2 times as big as the United States. Yet except for only a few hundred square miles along the coast, the entire continent is continually covered with ice. No, we can’t really call a … Read more

If you hear someone describing a bad winter hailstorm, you can be pretty sure he’s either lying or mistaken, for it almost never hails in winter. Hailstones rarely form unless a thunderstorm is brewing. Hail is caused by the same cloud conditions that usually cause rain in a thunderstorm, except that with hail, the raindrops … Read more

A blizzard is not just a heavy snowstorm. The word “blizzard,” which is used only in the United States, refers to a snowstorm with very strong, cold winds that whip the snow into a fine white dust. Some blizzards may bring less snow than an average snowfall.

Weather records that include the size of a snowfall have been kept for only about 100 years, so we don’t know the size of the heaviest snow of all time. But in 1921, the heaviest daily snow on record struck Silver Lake, Colorado, dumping 76 inches of snow on that town in 24 hours! The … Read more

When you hear of a “petrified forest,” you might think of trees shaking in the wind, the way a person shakes when he’s frightened, or “petrified.” Actually, this word comes from a term that means “stone.” A petrified tree is really a tree that has been turned into stone! The largest collection of petrified trees … Read more

Niagara Falls, on the border between New York State and Canada, pours about 620,000 tons of water over its edge each minute. But in March, 1847, the waterfall almost came to a standstill. The water of the Niagara River froze over until only a trickle of water was pouring over the falls. People rode nearly … Read more

In some places in the United States, the tap water doesn’t allow soap to form lather, and cannot be used for washing without the addition of chemicals called “water softeners.” This kind of water is called “hard” water, and it’s caused by certain minerals in the water. Sometimes water contains molecules of carbon dioxide gas, … Read more

Weather experts have a tough time finding out exactly how much rain has fallen in some distant parts of the world, so no one is really sure what is the heaviest single rainfall of all time. But we know that an island in the Indian Ocean once received more than six feet of rain in … Read more

Meteorologists, or weather experts, measure rainfall and snowfall in inches. They let falling rain collect in a cylinder, and can tell how many inches have fallen by seeing how far the rain fills up the cylinder. If your weatherman says that an inch of rain fell on your town, it means that if the ground … Read more

It might sound strange to say that rain keeps the earth dry, but that’s exactly what it does. The process that results in rain gathers moisture from the air and concentrates it in clouds, which later deposit the water in the form of rain. If this moisture didn’t condense to form rain, then the atmosphere … Read more

Waves in the deep parts of the sea move like ripples on the surface of the water. When they near land and enter shallow water, they slow down, because deep water always moves faster than shallow water. Waves also grow higher as they near a shore, for in effect the sea bottom is “rising” as … Read more

Tidal waves have nothing to do with the tides, which are caused by the gravity of the moon and the sun. A better term for a tidal wave is a seismic sea wave, or a tsunami, a word which comes from Japan, where tidal waves are common. Tsunamis are caused by earthquakes under or near … Read more

Ocean waves are caused by winds that form ripples in the surface of the water, then gradually increase the height of these ripples until they become waves. Water at the surface of the sea may look like it’s moving along with the waves, but actually it’s moving up and down in the same spot! As … Read more

Since there are five oceans and many more seas in the world than seven, you may have wondered what people mean when they say the “seven seas.” Don’t go looking on a map for the seven seas, because you’ll never find them. “Seven seas” is just an expression meaning all the oceans and seas of … Read more

The Atlantic and Pacific Oceans are more than 2,500 miles apart in most of the United States. But in some places in Central America, the world’s two biggest oceans are separated by less than 50 miles of land. Panama is the narrowest part of Central America, but there are no mountains in Panama that offer … Read more

Sea water is actually colorless. If you held ocean water in your hands, you would see that readily enough. But the surface of the sea absorbs all except the blue rays of the sun. These rays are reflected by the water, and make the ocean appear blue. Minerals and tiny organisms in water make the … Read more

An oasis is a green, fertile area surrounded by desert. Some oases are supplied with water by underground springs. Others receive their water from streams that bring rainwater down from nearby mountains. An oasis usually has palm trees and tropical fruits and vegetables. Some small oases are used as resting points for travelers crossing the … Read more

When you think of a desert, you may picture vast areas of totally barren, shifting sands. But only a small part of most deserts is completely barren. By and large, most of the world’s deserts look just like the parts of the United States that we call deserts, with rocks, cliffs, and a great variety … Read more

The Sahara Desert, whose name comes from the Arab word sahra, meaning “wilderness,” is by far the biggest desert on earth. Though the exact boundaries of the Sahara are hard to define, this African desert stretches more than 3,000 miles at its longest point, and in most places is over 1,000 miles wide. The Sahara … Read more

Scientists used to believe that the sand in the Sahara Desert was left there by sea water that once covered the area. It is true that much of the Sahara was covered with water more than 100 million years ago. But we now know that the Sahara’s sand is much newer than that. The Sahara’s … Read more

Rain falls once in a while even in the hottest parts of the desert. The average rainfall in the Sahara Desert, the world’s largest, is from five to ten inches per year in most places. But one region of the Sahara receives just one-tenth of an inch of rain each year, and another part of … Read more

On clear, cloudless nights, the earth loses its heat more quickly than on cloudy nights. Therefore, the earth and the atmosphere get cooler much sooner. Since cooler air usually brings a heavy dew, you can be pretty sure that when you see a heavy dew, the sky is clear and therefore good weather lies ahead. … Read more

Ever since ancient times, people have been saying that dew “falls,” but it’s not true. Dew forms where you find it, on plant leaves, not in the clouds. This is how it happens: At night, the air gradually cools off. Cool air holds less water than warm air, so that when the temperature of the … Read more

You may have heard someone say, “It’s too cold to snow today,” but actually it can never be too cold to snow. Snow clouds form high in the air, where the temperatures are colder than it almost ever gets here in the United States. Two-inch snowstorms have fallen when the ground temperature was colder than … Read more

Hail or sleet is frozen rain, but snow is never formed as a frozen raindrop. Snow forms from ice crystals high above the earth. These particles turn into snow without first becoming rain. At the height that snow usually forms, the temperature is from 20 to 60 degrees below zero, far too cold for water … Read more

The average city in the United States might receive 25 to 45 inches of rain in a year. New York receives about 43 inches, and Dallas about 32 inches. But a mountainous region on the island of Kauai, in Hawaii, receives 460 inches of rain in an average year. In Kauai, the wettest place on … Read more

Water in one place certainly tastes different from water in another place, and there isn’t a person alive who hasn’t said, “This water tastes good.” But water is not only colorless and odorless, it’s really tasteless too! That is, pure water is tasteless. But you’ve probably never tasted pure water in your life. All water … Read more

Inertia is the tendency of objects that are at rest to remain at rest, or of moving objects to continue moving, unless they are acted upon by some outside force. This concept of physics was discovered by the Italian scientist Galileo in the 16th century. Because of the property of inertia, an object set on … Read more

A gas, a liquid, and a solid are simply different forms of the same thing. And that form is determined by how hot that substance is and how much pressure is applied to it. Heat can turn a solid into a liquid by giving its molecules more energy and motion, and then turn the liquid … Read more

A constellation is a group of stars that seem to form the shape of an animal, person, or object when viewed from the earth. The term comes from the Latin word stella, which means “star.” But the stars in a constellation only appear to form a shape, and may not even belong to the same … Read more

The spring of 1816 did not bring the usual warm weather to the eastern United States. In fact, winter seemed to stretch right through spring, and then summer itself didn’t arrive! In Massachusetts, the temperature dropped to 30 degrees Fahrenheit in early June, and a fairly heavy snow fell. Crops and livestock perished. Then the … Read more

A year is the time it takes the earth to go around the sun, and a day is the time it takes the earth to rotate once on its axis. The earth now rotates 3651/4 times during each trip around the sun. But by studying the remains of plants and animals that lived millions of … Read more

For people who live north of the equator, the shortest day of the year falls around Dec. 22. This day is called the winter solstice. (The longest day of the year is called the summer solstice, and falls around June 21.) But the winter solstice falls at the beginning of winter, not in the colder … Read more

The equator is an imaginary circle around the earth, an equal distance from the North and South Poles. Since the weather gets warmer as you travel away from the polar regions toward the equator, you would think that the equator is the hottest place on earth. But there are some places on the equator where … Read more

Surprisingly, the earth’s distance from the sun has nothing to do with weather! The earth’s path around the sun is not a perfect circle, but an ellipse, or egg shape. The earth is actually nearest the sun around January 2, when it’s “only” 91,402,000 miles away. This point is called the perihelion. At the earth’s … Read more

If we use “world” to mean the universe and not just the earth, then the largest volcano that we know about is on the planet Mars. This huge mountain, called Olympus Mons, is about 370 miles across, and its peak stands 18 miles above the surrounding land. Mount Everest, Earth’s tallest mountain, is less than … Read more

A solar eclipse occurs when the moon passes directly between the sun and the earth. When the earth passes directly between the moon and the sun, a lunar eclipse occurs. A lunar eclipse can happen only when the moon is full, because then it is on the other side of the earth from the sun. … Read more

As the moon travels around the earth, it passes between the earth and the sun once each month. The orbit of the moon around the earth is not in a direct line with the earth’s orbit around the sun, so the moon usually doesn’t pass directly in front of the sun. But when it does, … Read more

The brightest of all the stars in our sky is Sirius, which is located in the constellation Canis Major, the Great Dog. For that reason, this star is also known as the Dog Star. Ancient astronomers noticed that Sirius rose with the sun late in the summer. That’s why we call the hot days of … Read more

There certainly is gravity in space! If there wasn’t, the moon wouldn’t revolve around the earth, and the planets wouldn’t revolve around the sun. The strength of the force of gravity between any two objects depends on two factors: the mass of the two objects and the distance between them. The heavier the objects are, … Read more

On Earth, clouds are made of water droplets and ice particles adrift in the atmosphere. Of all the planets in the solar system, only Earth has large amounts of water, so our planet is the only one with clouds, as we know them. But some planets have clouds made of things other than water. The … Read more

There are really two kinds of planets in our solar system. One kind is called a terrestrial planet because it is very much like Earth. The other is called a jovian planet because it is more like Jupiter. When the solar system formed, the planets took shape out of clouds of dust and gas. Those … Read more

We call our moon “the moon” because it’s the only moon that earth has. But some of the other planets have moons too. And all of the planets that do have moons have more than one! Mars and Neptune each have two moons, Uranus has five moons, and Saturn has ten. Jupiter, the largest planet, … Read more

The moon never changes its color, but there have been times when the moon did look blue to people on earth. In 1950, a huge forest fire in Canada sent tons of tiny cinders into the atmosphere. These cinders absorbed some of the sun’s rays that bounce off the moon and reach earth, but didn’t … Read more

Almost everything in the universe travels in a circular path. The moon goes around the earth, the earth goes around the sun, and even the sun revolves around the center of our galaxy. This is because of two basic laws of science. First, an object moving in space, where there is no air to slow … Read more

Sunspots look like dark, cool splotches on the bright surface of the sun. But these spots only look cool because they’re cooler than the areas around them. The surface of the sun is about 11,000 degrees Fahrenheit, while the gases over a sunspot may be “only” 7,200 degrees. Sunspots are caused by the magnetic fields … Read more

The earth rotates around its axis, an imaginary line drawn through the North and South Poles. The other planets also spin around their axes, but not all planets spin in the same direction that the earth spins. The earth rotates in the same direction that it moves around the sun. Venus spins in the opposite … Read more

In ancient times, as people watched the sun move across the sky each day, they thought that the sun traveled around the earth. Scientists later found out that the sun remains in one place while the earth and the other planets travel around it. But we know now that the sun moves too! The sun … Read more

Venus is not only warmer than the earth, it’s warmer than any other planet in the solar system. Man has already landed space probes on Venus, and found that the temperature at the surface of the planet is about 900 degrees Fahrenheit! The planet Mercury, which is closer to the sun than Venus, is never … Read more

It may sound impossible, but it’s easy. You look into the past every night when you see the stars! We measure the distance between stars in light- years. A light-year is the distance that light travels in one year, about six trillion miles! When you look at a star that is ten light-years away, you’re … Read more

Mercury is the closest planet to the sun, less than half as far from the huge ball of heat as the earth is. You would think that it gets pretty hot on Mercury. But strangely enough, part of the planet is much colder than earth! Like all planets, Mercury spins on its axis, so that … Read more

Before the first man landed on the moon, scientists had come up with three possible ways that the moon might have been formed. First, it could have formed out of the same gas cloud that formed the earth. Or it could have broken off from the earth many millions of years ago. Or perhaps the … Read more

So far, we know of nine planets in our solar system. Some astronomers think that there may be a tenth planet beyond the orbit of Pluto, the farthest known planet from the sun. And others think there was once a tenth planet that doesn’t exist anymore! The space between Mars, the fourth planet from the … Read more

We know there are nine planets. But in ancient times, people knew of only six: the earth and the five planets that can be seen without a telescope. Venus, the brightest planet in our sky, was named after the Roman goddess of love and beauty. Mercury, the fastest- moving planet, was named after the fleet-footed … Read more

A galaxy is a large grouping of stars, such as the Milky Way galaxy in which we live. Scientists have figured out that a galaxy contains from one billion to one trillion stars. And they also believe that there are about ten billion galaxies in the universe. So, there may be as many as 10,000,000,000,000,000,000,000 … Read more

Shooting stars look like blazing stars flying through the distant heavens. But a shooting star is not a star at all, and it’s not very distant, either! In ancient times, people thought that shooting stars were just part of the weather, like lightning or fog. But we know now that shooting stars are actually objects … Read more

Of the billions and billions of stars in the heavens, only about 6,000 can be seen from the earth without a telescope. And about a quarter of these 6,000 stars cannot be seen from most lands north of the equator. Some of the stars that we can see look much brighter than others. Scientists call … Read more

Most stars in the universe are bigger than the sun, and some are even bigger than the entire solar system. But not all stars are as big as the sun, or even as big as the earth. The smallest kind of star, called a white dwarf, may be only about a thousand miles in diameter, … Read more

As a big star runs out of fuel to burn, it begins to shrink. And as it shrinks, all its atoms are crushed together into a smaller and smaller area. Then, even the particles that make up the atoms are squashed together too. The result is a small, very heavy ball of atoms called a … Read more

A type of star called a black hole isn’t really black. It’s giving off light just like any other star. But this light can never reach us, so the star looks “black.” Imagine a huge star that runs out of gas to burn after billions of years of shining. As the star runs out of … Read more

In 1967, scientists detected pulsing signals coming from far-off outer space. These bursts of energy reached earth with such a regular pulse rate that it seemed they were being sent by beings on another world. At first they were called LGMs, for “Little Green Men.” Later, it was discovered that these signals came from stars … Read more

There’s no way to say how long the “average” star lives, because there’s really no such thing as an “average” star. Some stars are so small that their diameter is only 1/70,000 the diameter of the sun, while others have a diameter a thousand times larger than the sun’s. Stars “die” in different ways too. … Read more

In 1961, astronomers detected a very powerful source of energy in space. When they looked through a telescope to try to find that energy source, they found an object that looked like a faint star. But they knew the object was giving off far too much energy to be a single star. They named this … Read more

The space between planets, or between stars, only appears to be empty. Actually, it’s filled with tiny particles of gas or dust too small to be seen. In fact, about ten percent of all the matter in our galaxy is gas and dust particles floating through space. But these particles are scattered very thinly through … Read more

No one can be certain, because no one can see the entire universe. But so far, the farthest star from earth that scientists have found is about ten billion light-years away. Since one light-year is equal to six trillion miles, then the farthest star from earth that we know about is around 60,000,000,000,000,000,000,000 miles away! … Read more

The weight of an object is really a measure of the force of gravity exerted on it by the earth. So bodies such as the earth and the moon don’t really “weigh” anything. But the earth and the moon do have mass, which is a measure of how much matter these bodies are composed of. … Read more

Scientists have tried to figure out how long the universe will exist, but they haven’t been able to agree with one another yet. Some scientists believe the universe will go on forever, even after all the stars are burnt out. The universe will then be completely dark and cold for the rest of time. But … Read more

Although there’s no way to be really sure, scientists have found a clever way to figure out the age of the universe, or at least to estimate how long it’s been around in its present form. Many scientists believe that the universe began with a tremendous explosion that sent all matter flying out into space … Read more