Universe

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

The Mary Celeste had a strange jinxed history ever since the time of her launching in 1861. Her first captain died after only a few days in command. Then she collided with another ship, damaging her hull and sinking the other ship. A few years later, she ran aground in Nova Scotia, and the man … Read more

Even though the Indians in the eastern part of North America used the white, purple, and black beads made from shells mainly as money, or wampum, they also used them to record important happenings in the tribe. Wampum beads were strung on belts to record each event in a story, and served as a reminder … Read more

In 1586, fifteen Englishmen settled Roanoke Island, off the coast of North Carolina, to establish England’s claim to the island. The following year, 117 additional settlers, men, women, and children, arrived, only to find that the original fifteen men had disappeared without a trace. Then three years later, in 1590, an English supply ship came … Read more

The huge stone slab at Mystery Hill in New Hampshire has long been a puzzle. Who put it there? Why? And what was it used for? The slab seems to be the top of a stone table, which may have been the scene of animal or human sacrifice. The grooves along the edge of the … Read more

You would have to be in an airplane looking down on the Nazca Desert in order to see this Peruvian puzzle. A series of gigantic pictures and designs have been made by removing the dark topsoil and exposing the lighter yellow soil underneath. The subjects are flowers, spiders, birds, snakes, and gods wearing halos. Some … Read more

At Stonehenge in England stand huge stones, some as high as 24 feet, arranged in three circles, one inside the other. They seem to be in that pattern for a reason, but until only recently, no one knew that reason. People could only guess that it was an ancient temple, which, according to radiocarbon tests, … Read more

Easter Island, a volcanic island in the South Pacific, is the site of a great mystery. Over 600 enormous stone heads, 2,000 years old, each carved from a solid piece of rock and with identical faces, stand over all the island. They rise from 10 to 40 feet above the surface and weigh up to … Read more

Machu Picchu, in Peru, is called “The Lost City of the Incas” lost, because it was only discovered in 1911. The temples, palaces, stairways, and terraces of this ancient walled Inca city show that its people worshipped the sun and were amazingly accurate as astronomers. One of the temples is so arranged that a wall … Read more

The ancient Egyptians buried their royalty in pyramids under millions of tons of rocks because they believed this would assure them of a life of peace and wealth after death, and an eternal life for their souls. The largest pyramid ever built, the Pyramid of Cheops, or the Great Pyramid, in Giza, Egypt, was probably … Read more

The ancient people of Egypt, Greece, and the Near East all had legends about imaginary creatures with human heads and animal-like bodies. These people built statues of these creatures, called sphinxes, to guard their temples and tombs. The sphinx in Greek mythology had the head of a woman and the body of a lion. She … Read more

Although people enjoy the custom of kissing under the mistletoe, this plant has another, not so pleasant habit. Just as a vampire sucks the blood of its victims, the mistletoe has a victim too, the plant on which it lives. In order to get nourishment, the mistletoe plant sends its root like structures into the … Read more

The small scarlet, white, or purple flowers of the plant called the scarlet pimpernel can give you a better weather prediction than the radio or TV weatherman. If you are in the woods in the morning and you see the flowers on this herb close up, you will know that rain or cloudy weather is … Read more

How about as tall as a ten-story building! Yes, there is a grass that grows that tall. It is called bamboo and grows in tropical areas. Even though these woody poles are so tall and so hard, they are actually in the same family as the grass in your yard. Some bamboo grows at an … Read more

The unusual baobab trees of Africa have trunks so wide, often approaching 35 feet in diameter that entire native families live in them. These trees are second in size only to the giant sequoias of California, but they have such a soft pulp inside their trunk that they can easily be hollowed out and used … Read more

Trees grow up because that is where the light is, and they need the light in order to continue growing. Like most plants, trees grow from seeds and have roots, stems, and leaves. A seed sends its roots down into the ground when it begins to grow, to take minerals and water from the earth … Read more

The Bible tells of two sacred trees in the Garden of Eden, the Tree of Life and the Tree of Knowledge. Adam and Eve were permitted to eat the fruit from any tree in the Garden of Eden except the fruit from the Tree of Knowledge, since God did not want them to have the … Read more

In the Methusaleh Grove, high on the windswept White Mountains near Bishop, California, grow the oldest living things on earth, over 4,000 years old. These are the bristlecone pines, also known as “living driftwood” because of their gnarled and bent appearance. The bristlecone pine is a bushy evergreen that got its name from the long, … Read more

The rubber belt is a name given to the area where the hevea, or rubber tree, grows. This tree needs a very rich deep soil and a climate that is hot and moist. Those are exactly the conditions about 700 miles above the Equator and 700 miles below it. These ten degrees of the Equator … Read more

Rubber comes from a milky white juice which some trees and plants have instead of sap. This liquid, called latex, can be found in the roots, stems, branches, bark, leaves, and fruit of over 400 different plants. Most latex, however, comes from the inner bark of the hevea, or rubber tree, of Brazil. To get … Read more

The smells in flowers come from special oils that are produced in the petals as the plant grows. When this oil evaporates, which it does very easily, it gives off a fragrance which we can smell. Various combinations of chemicals in the oils of different flowers result in a variety of fragrances. Some are pleasant, … Read more

Many flowers have petals which are open during the day, but which close up at night. These flowers are reacting to light or temperature changes. Other flowers, however, remain open around the clock, while still others have unusual opening and closing habits. But these habits are all related to light or temperature changes. Here’s how … Read more

Cactuses are thrifty plants that live in dry regions. They may not get much moisture where they live, but they manage to make the most of what they do get. Since the cactus’s long roots lie close to the surface of the ground, they can catch water from desert rains. And since the roots have … Read more

The meanest kind of plant life is the strangler tree, which comes in several varieties. One example is the strangler fig tree of Brazil, whose fruit provides food for native birds. Once a bird has eaten a fig, it may fly off with the fig seed in its mouth. It often deposits that seed at … Read more

Someone lost in a forest need only study the trees around him carefully to find his way. In our hemisphere, he will find that the side of the tree with the most leaves and branches is the south side. Also, by checking the tops of the trees, he will find that they lean to the … Read more

Some plants depend on animals such as birds or insects to carry their seeds away to start new plants; others just drop their seeds onto the ground about them, and new plants soon sprout, or are carried to other locations by the wind. But a number of plants, like the squirting cucumber, have a strange … Read more

The beautiful water hyacinth, with its ten-inch lilac flowers, is just too much of a good thing. This floating plant has roots which hang freely in the water, as opposed to other water plants whose roots are imbedded in the mud. In just one season, a single piece of a floating root can start off … Read more

The blue moonwort, a member of the primrose family, can. It grows on the Swiss Alps, where it is covered by several feet of ice and snow throughout the winter. This does not seem to discourage the moonwort at all. With the coming of spring, the moonwort’s roots drink up a bit of water from … Read more

Although we use tomatoes as vegetables, they are actually classified by botanists as fruits because they contain seeds inside their juicy, pulpy tissue. In fact, the tomato is considered to be a berry, much like the strawberry, blackberry, and raspberry. Aside from tomatoes, several other foods that we usually term vegetables are considered fruits. These … Read more

Leaves are actually little “factories” that manufacture food to help the plant grow. In the spring and summer, these factories run at top speed, taking in carbon dioxide from the air and water from their roots. Then sunlight enters the leaf and sets the factory in motion. But a leaf could not begin its manufacturing … Read more

Most trees begin life as a seed and continue to grow as long as they live, some for hundreds or even thousands of years. The history of a tree, its age, plus events that took place as it grew, can all be revealed by studying its trunk after it is cut down. A tree grows … Read more

Far from it! In addition to the obvious poison mushrooms, poison oak, and poison sumac, there are about 700 other poisonous, or toxic, plants which are usually avoided by people and animals. Common garden shrubs and plants such as azaleas, rhododendrons, mountain laurel, and foxglove are completely poisonous. There is cyanide in cherry twigs and … Read more

Poison ivy is a vine that straggles over the ground or winds itself around tree trunks, or even forms its own bush if it has nothing to wind itself around. The poison ivy leaf is made up of three leaflets. These leaflets contain poisonous oil that irritates the skin of anyone touching them. This oil … Read more

Yes! Plants which trap and eat insects and other small animals are called carnivorous, or meat-eating, plants. These carnivorous plants are usually found in areas where the soil does not have a good supply of minerals to nourish the plants. So the plants get these needed minerals from living victims, usually by digesting the soft … Read more

In the South American country of Venezuela, in a huge, thick, “lost” rain jungle sit several mesas, high, flat-top plateaus with steep sides. These mesas are in such a remote area of the jungle that it takes four days of travel by water to reach them from any settlement. One of these mesas, called Auyan-tepui, … Read more