Tell me why

                        WHAT CAUSES THE WAVES? If you've ever spent some time near a body of water, then you noticed that on a calm day there are very few waves in the water, and on a windy or stormy day there are many waves. This, of course, explains what causes waves in the water. It is the wind. A wave is a way in which some form of energy is moved from one place to another. Some sort of force or energy must start a wave, and the wind provides that energy in the water. When you watch the waves move, one after the other, the water seems to move forward. But if there is a piece of floating wood in the water, it will not move forward as the waves seem to do. It will only bob up and down with the waves. It moves only when the wind or tide moves it. Then what kind of motion is taking place in a wave? A water wave is mostly the up-and-down movement of water particles. The movement passes on toward the shore, but not the ...

                              WHICH IS THE DEEPEST OCEAN?                In many ways, the oceans still remain a great mystery to us. We don't even know how old the oceans are. It seems certain that in the first stages of the earth's growth no oceans existed.                Today, man is exploring the bottoms of the oceans to learn more about them. Covering the floor of the ocean to a depth of 3,660 metres  is a soft, oozy mud. It is made up of the limy  skeleton  of tiny sea animals. The floor of the deep, dark regions of the sea, where the water is more than four miles deep, is covered by a fine, rusty-colored ooze called "red clay." It is made up of tiny parts of skeletons of animals, the coverings of tiny plants, and volcanic ash.            ...

                                WHY IS THE OCEAN SALTY? Every now and then, we come across a fact about our earth which mystifies us and for which no answer has yet been found. Such a fact is the existence of salt in the oceans. How did it get there? The answer is we simply don't know how the salt got into the ocean! We do know, of course, that salt is water-soluble, and so passes into the oceans with rain water. The salt of the earth's surface is constantly being dissolved and is passing into the ocean. But we don't know whether this can account for the huge quantity of salt that is found in oceans. If all the oceans were dried up, enough salt would be left to build a wall 180 miles high and a mile thick. Such a wall would reach once around the world at the Equator! Or put another way, the rock salt obtained if all the oceans dried up would have a bulk about 15 times as much as the entire con...

                               WHY ARE THERE DIFFERENT KINDS OF CLOUDS? Here is how clouds are formed: Warm air, laden with moisture, rises into the sky. When it gets to a certain height, the warm air cools. At the cooler temperatures it can no longer hold all its moisture in the form of water vapor. So the extra moisture changes into small drops of water, or bits of ice, and this forms clouds. No two clouds are exactly alike, and they are always changing their shape. The reason we have different types of clouds is that cloud formation takes place at different heights and temperatures. And clouds will be com- posed of different particles, depending on their height and temperature. The highest clouds are called "noctilucent" clouds. They may be up as high as 30 to 50 miles! The next highest are called "nacreous," or "mother-of-pearl" clouds. They're 12 to 18 miles high. They are very thin, beau...

                                                            WHAT IS A COMET? At one time, the appearance of a comet caused people to tremble with fear. They believed that comets were evil omens foretelling plagues, wars, and death. Today, we have a pretty good idea of what comets are, though we still don't have all the answers about them. When a comet first appears, it is seen as a tiny point of light, though it may be thousands of miles in diameter. This point of light is "the head," or nucleus, of the comet. Scientists think it is probably made of a great swarm of bits of solid matter, combined with gases. Where this matter originally came from is what is still a mystery. 21 [8:19 am, 24/11/2024] Sher Singh: As the comet approaches the sun, a tail usually appears behind it. The tail consists of very thin gas...

                                             WHAT ARE FALLING STARS? F or thousands of years men have looked up at "falling stars" and wondered what they were and where they come from. At one time it was believed that they came from other worlds. Today we know that they are not "stars" at all. We call them "meteors." They are small, solid bodies which travel through space, and which may also pass through the earth's atmosphere. When meteors come within our atmosphere, we can see them because they leave a fiery train of light. This is caused by the heat made by the friction, or rubbing, of air upon their surfaces. Strangely enough, most individual meteor particles are quite small, about the size of a pinhead. Occasional meteors weigh many tons. Most meteors are destroyed entirely by heat as they pass through the earth's atmosphere. Only the larger meteor ...

                               WHAT IS THE BRIGHTEST STAR? Have you ever looked up at the sky and tried to find the brightest star? You may imagine that the number of stars you can see is countless. But the most that can be seen without a telescope are about 6,000 stars, and one-quarter of them are too far south to be seen in North America. Ever since the days of the Greek astronomers, 2,000 years ago, the stars have been divided into classes according to their magnitude or bright- ness. Until the invention of the telescope, only six magnitudes, or degrees of brightness, were recognized. Stars of the first magnitude are the brightest, and stars of the sixth magnitude the faintest. Stars fainter than the sixth magnitude cannot be seen without a telescope. Today, stars can be photo- graphed with modern telescopes down to the 21st magnitude. A star of any given magnitude is about two and a half t...

                                 WHAT IS THE MILKY WAY? There is probably nothing more mysterious and wonderful-looking in the sky than the Milky Way, stretching like a band of jewels from one end of the sky to the other. In ancient times, when people gazed at this spectacle, they were filled with the wonder and beauty of it just as you are. But since they didn't really know what it was, they made up all sorts of strange and beautiful explanations of the Milky Way. For example, in early Christian times, people thought it was a pathway for the angels, so they could go up to heaven on it. Or they imagined it was an opening in the heavens, so that we here on earth could have a glimpse of the glory that existed beyond. Knowing the facts about the Milky Way, as we do today, doesn't remove any of the wonder of it. The facts are just as amazing as any "made-up" idea! Our galaxy is shaped roughly...

                                     WHAT IS A CONSTELLATION? Have you ever looked at the stars and traced out squares, letters, and other familiar figures? In nearly all parts of the world, people of long ago did this and gave names to the group of stars they observed. Such a group is called "a constellation," from the Latin terms meaning "star" (stella) and "together." The names of the constellations in use today have come down to us from the times of the Romans and from the even more ancient Greeks. What the Greeks knew about the stars came partly from the Babylonians. The Babylonians named some of their star figures after animals and others after kings, queens, and heroes of their myths. Later, the Greeks changed many of these Babylonian names to the names of their own heroes such as Hercules, Orion, and Perseus. The Romans made further changes. The same ancient names are st...

                                                    WHY ARE ECLIPSES SO RARE? When the moon in its journey around the earth passes directly between the earth and the sun, it casts its shadow on the surface of the earth, and an eclipse of the sun takes place. An eclipse of the sun occurs only when the moon is new, for then the moon is on that side of the earth facing toward the sun. Then why isn't there an eclipse of the sun every time there's a new moon? The reason is that the path of the moon around the earth does not lie directly in line with the orbit of the earth about the sun. In its 29-day trip around the earth, the moon passes sometimes above and sometimes below the path of the earth. An eclipse of the sun can be total, annular, or partial. If the moon hides the sun completely, the eclipse is total. But the moon is not always t...

                                 WHAT IS THE EARTH MADE OF? Man is now preparing to explore the moon and other planets-and he till doesn't know exactly what his own earth is made of! A sort of rough answer to this question would be: The earth is a big all, or sphere, made mostly of rock. Inside the earth the rock is melted, but me outside cover is hard rock. Less than one-third of the earth's surface is and and more than two-thirds are water. Now let's consider this in a little more detail. The outside of the earth s a crust of rock about 10 to 30 miles thick. This crust is sometimes called "the lithosphere." The high parts of this crust are the continents, and the low parts of it hold the waters of the oceans and the great inland seas and lakes. All the water on the surface, including the oceans, lakes, rivers, and all the smaller streams, is called "the hydrosphere." Men have ...

                                        WHY DO SUNSETS LOOK RED? A beautiful red sunset, the colors warm and glowing, is one of the love- liest sights we can imagine. And sometimes, when we look at it we might say, "See how red the sun is!" But, of course, we know that the sun itself hasn't become red or changed in any way. It merely looks that way to us at that particular time of day. In fact, at that very moment people are looking at that same sun thousands of miles to the west and it doesn't look red to them at all. What produces the colors of a sunset is the distance that the sunlight must travel through our atmosphere. The lower it is, the more of our earth's atmosphere does that light travel through.  But first, let's remind ourselves that sunlight is a mixture of light of all colors. Normally, this mixture of light appears as white to our eyes. But the atmo...

                                               WHAT KEEPS THE SUN SHINING? It may be hard for you to believe, but when you look at the stars that shine at night and the sun that shines by day, you are looking at the same kinds of objects! The sun is really a star. In fact, it's the nearest star to the earth. Life as we know it depends on the sun. Without the sun's heat, life could not have started on earth. Without sunlight, there would be no green plants, no ani- mals, no human beings. The sun is 93,000,000 miles from the earth. The volume, or bulk, of the sun is about 1,300,000 times that of the earth! Yet an interesting thing about the sun is that it is not a solid body like the earth. Here is how we know this: The temperature on the surface of the sun is about 6,000 degrees centigrade. This is hot enough to change any metal or rock into a gas, s...

                           WHY IS THE SOLAR SYSTEM THE WAY IT IS? As far as we know, there is no reason why the solar system is arranged exactly as it is. It might have been arranged differently, just as there are other solar systems in the universe arranged differently. This has to do with the way it originated. But man has discovered certain laws of nature that seem to keep the solar system in its present pattern. Earth, like the other planets, follows its path, or orbit, around the sun. The period of time that the earth takes to go around the sun is called a year. The other planets have orbits larger or smaller than the earth's. How this solar system came to be and how the planets came to have the size, location, and orbits they have, astronomers cannot fully explain. But they have two main types of theories. One type of theory suggests that the formation of the planets was a part of the gradual chan...

                     How big is the universe?                          It is impossible for the human mind to conceive a true picture of the size of the universe. We not only don't know how big it is, but it is hard for us even to imagine how it might be. If we start from the earth and move out, we'll see why this is so. The earth is part of the solar system, but a very tiny part of it. The solar system consists of the sun, the planets that revolve around it, the asteroids, which are tiny planets, and the meteors.  Now, this whole solar system of ours is only a tiny part of another, much bigger system called "a galaxy." A galaxy is made up of many millions of stars, many of which may be much larger than our sun, and they may have solar systems of their own. So the stars we see in our galaxy, which we call "the Milky Way," are all suns. They are all so fa...