Universe

Since ancient times, though the day has been divided into 24 hours, each hour has not always had 60 minutes, as we measure them. The ancient Greeks divided the daytime into 12 hours, but they measured a day from sunrise to sunset. So, the longer a day was, the longer was each hour in it. […]

The Greek Eratosthenes, who lived around 250 B.C., was the first man we know of to figure out the size of the earth. Yet he never traveled around the earth, nor did he have any of today’s measuring equipment. How, then, did he do it? Eratosthenes used Euclid’s principles of geometry to solve the problem. […]

E = mc2 is a formula that shows, in mathematical terms, the relationship between energy and mass. In this formula, E is energy, m is mass, and c is the speed of light. The number 2 to the upper right of the c means that c is squared, or multiplied by itself. This formula, first […]

Every gallon of sea water contains an average of four ounces of salt. And there’s enough salt in the world’s oceans to cover the entire surface of the earth with a layer of salt more than 147 feet thick! But scientists aren’t quite sure how all that salt got into the oceans. Rocks that contain […]

Millions of years ago, when much of the earth was a swampy forest, billions of plants and animals died and fell into the shallow water. The oxygen, hydrogen, nitrogen, and carbon in these living things were acted upon by bacteria and pressure over thousands of years, freeing gases from the decayed matter and leaving behind […]

In cold weather, low temperatures cause the body to lose heat. But the wind also takes heat from the body, so a temperature reading doesn’t always tell us how cold it really feels. The wind chill factor was devised by weathermen to show how the temperature and the wind combine to produce the feeling of […]

You’ve seen quicksilver many times without knowing it. The thermometer you use to take your temperature contains a drop of quicksilver, for quicksilver is just another name for mercury! The quick in quicksilver came from an old word that meant “living.” In earlier times, mercury was called “living silver,” because of the odd way it […]

The moon gives off no light of its own, but merely reflects the sunlight that reaches it. So only half of the moon can be lit up by the sun at any one time. We on earth can see only that portion of the moon that is lit by the sun. Sometimes the moon, sun, […]

The word “archipelago” comes from two Greek words: archos, meaning “chief,” and pelagos, meaning “sea.” The Greeks originally used the word archipelagos for the Aegean Sea, which washes against the shores of Greece and was their “chief sea.” Since the Aegean Sea is studded with many islands, the word “archipelago” came to mean any sea […]

The famous Cliffs of Dover, which lie along the shore of England beside the English Channel, are as white as chalk, as they’re made out of basically the same material as a piece of blackboard chalk! Chalk consists of the remains of tiny sea organisms and fragments of sea shells. These fragments are continually washed […]

Greenland, the largest island in the world, is just about the most ungreen place on earth! Most of this island, which is more than three times as large as Texas, is continually covered with ice and snow. This ice sheet is two miles thick in some places. There are no forests in Greenland, but there […]

About 70 percent of our planet is covered with water. Including all seas and oceans, water covers about 140 million square miles of earth, with an average depth of 11,600 feet. That means that the total amount of water on earth is 315 million cubic miles! If all the water on earth were spread over […]

Sometimes an island appears out of nowhere, when a volcano under the ocean erupts or when the ocean bed buckles and pushes land to the surface of the water. But islands can disappear too, when the ocean bed buckles and pulls land under the water. Falcon Island, which is really the peak of a volcano, […]

Earthquakes with a Richter scale reading of more than 5.5 have caused great loss of life and property, and quakes with a 7.0 reading almost always cause massive destruction. A number of quakes that took place during this century have measured over 8.0 on the Richter scale. The two most powerful measured 8.9 on the […]

Scientists measure the strength of an earthquake with a machine called a seismograph, which takes its name from seismos, the Greek word for an earthquake. The seismograph basically consists of a very delicate metal arm with a needle or pen at the end, which rests on a moving drum of paper. When the earth is […]

You won’t find a place called Gondwanaland on any map of the world. Gondwanaland, or simply Gondwana, is the name scientists use for one of the huge land masses, that existed before the continents began to drift apart. According to some scientists, all the continents once formed a single land mass, called Pangaea. This land […]

If you wanted to get away from it all, the best place on earth to go would probably be a small island in the South Atlantic Ocean called Bouvet Island. This island was discovered in 1739, but not a single person lives there today. Bouvet lies about 1,050 miles away from the nearest piece of […]

The expression, “it’s a wide, wide world,” is certainly true, for the surface area of our planet is about 200 million square miles! But a more important question is: How much of the earth’s surface is usable by man? About three-quarters of the earth’s surface is covered by water. Of the 57 million or so […]

Water cannot burn. If you see a fire burning on top of a body of water, you can be sure that there must be something floating on top of the water. For instance, oil can float on top of water, and this layer of oil can indeed burn.

Travelers in swampy areas have often seen a strange bluish flame that appears suddenly, moves along the ground, and disappears as suddenly as it appeared. Sometimes, this light is seen in graveyards too. In earlier times, people thought that the flame was a spirit, or a light carried by a spirit, and many superstitions grew […]

Each time you take a breath, you breathe in about one pint of air. A standing or sitting adult takes from 16 to 20 breaths a minute, but an adult lying down may take only 13. And a child may take 35 breaths per minute. On the average, a person takes about 22,000 breaths each […]

The answer to both questions is yes, if you calculate the date according to calendars other than the one we use! We number our years from the supposed date of Christ’s birth. But Jews count their years from the date of creation, which ancient scholars claimed took place in the year 3761 B.C. So, the […]

In 46 B.C., Roman ruler Julius Caesar put a new calendar into effect, which came to be known as the Julian Calendar. The Romans thought that the year was 365.5 days long, so they made an ordinary year 365 days and added an extra day every fourth year, or leap year. But by the year […]

We’ve all looked at the globe and studied the shape and position of the land masses called continents. But the size and the shape of the continents have not been the same during all of the earth’s history. Parts of the continents were once covered with water, while parts of the sea were once dry […]

The earth is about 4.5 billion years old, but life did not exist on this planet until about 2 billion years ago, when certain kinds of bacteria and algae began to appear. Land plants did not appear until about 430 million years ago; reptiles, 300 million years ago; and modern mammals, 75 million years ago. […]

No, the earth is not a perfect sphere. It’s actually squashed in a bit at the poles, and widest at the equator. The diameter of the earth, an imaginary line drawn through the center of the earth from one side to the other, is about 7,926 miles at the equator, but only about 7,900 miles […]

Nothing can burn on earth without the presence of oxygen. As what we call “fire” or “burning” is a chemical reaction in which atoms of oxygen combine with atoms of carbon from the fuel, the substance being burned, to produce carbon dioxide, light, and heat. Since fire needs oxygen, and there is almost no oxygen […]

The earth’s atmosphere is the envelope of gases that surrounds our planet and revolves with it. Most of the gases are within about 300 miles of the earth’s surface, but a thin atmosphere extends some 22,000 miles! Up to a height of 60 miles above the earth, the atmosphere is mostly nitrogen and oxygen. About […]

No, it’s not really very cold, and it’s not really very hot, either. It all depends on where in the atmosphere you are! The earth’s atmosphere consists of layers of gases. The lowest layer, called the troposphere, extends to a height of seven miles, and this is the layer in which all our weather takes […]

The tundra isn’t really a particular place on earth. It is a type of climatic region, just as a desert is. In fact, tundras are sort of “cold deserts”, vast, flat tracts of land near the Arctic region, the northernmost parts of Siberia, Scandinavia, Alaska, and Canada. A tundra is a cold, barren place, where […]

Sailors in the Mediterranean have long marveled at the image of distant castles hovering over the sea near the city of Messina, Sicily. But as the sailors neared the image, it moved away from them or completely disappeared. They thought this illusion was a trick played by an evil fairy named Morgan Le Fay. So […]

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 […]

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! […]

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, […]

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 […]

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 […]

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 […]

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. […]

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 […]

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 […]

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, […]

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 […]

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 […]

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 […]

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 […]

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 […]

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.

You probably have seen pictures of snowflakes, and heard that no two flakes are the same. Have you ever wondered how scientists examine snowflakes? After all, most flakes are only a fraction of an inch across, and melt as soon as a person touches them. Since 1940, scientists have had a clever way to study […]

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 […]

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 […]

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 […]

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, […]

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 […]

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 […]

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 […]

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 […]

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 […]

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 […]

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 […]