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Starfish belong to the same group of invertebrates that live in the sea.  These animals are echinoderms , which means " spiny skinned ". Starfish are flatter and have disk-shaped bodies, with a number of arms around the outside of the central body. Most starfish have five arms, but some species have as many as fifty!  If we turn a starfish, we'll see hundreds of tiny, sucker-like tubes waving about on the undersides of its arms. These are tube feet, and they are very useful to the starfish. The suckers on the tube feet can stick to rocks or shells. The starfish moves along by pushing out, or extending, the tube feet on one of its arms so that they will stick to a nearby rock or to the seabed. When the tube feet shrink, or contract, the starfish is pulled forwards. Each tube foot has little strength, but hundreds of tube feet together are much stronger. Starfish use their tube feet to pull apart the shells of clams and oysters so that they can eat the soft flesh...

Have you ever seen a jellyfish? It looks like an umbrella with projections, called tentacles, hanging down from the edges. The body of a jellyfish is like a hollow bag with thick sides. These sides have an "outer skin" and an "inner skin." Between these two "skins" is a jelly-like substance. This substance gives the jellyfish its shape. Jellyfish live in the sea, but they are not fish.  Fish have backbones and move forward by swimming. Jellyfish do not have backbones, and they move up and down in a unique way. They expand like an opening umbrella, then pull together again rapidly. This squeezes water out from beneath, and the jellyfish moves upward. Jellyfish eat small sea animals after stinging them with their tentacles.  The tentacles are covered with thorny threads. When another animal bumps into the jellyfish, these threads lash out like tiny, poisonous whips. The threads paralyze the victim, and the jellyfish then uses its tentacles to p...

12 October 1492 – Christopher Columbus discovers America - painting by John Vanderlyn. When we say "discovered " in such cases we usually have in mind a special meaning of the word. We want to say that people from one civilization came to an area where no one from their neighborhood had not been. As you probably know, the explorers often encounter people and a civilizations that are already in place which he "discovered". So why we don’t we say that these people found these places first? From the standpoint of western civilization, we say that Columbus discovered America because after his discoveries in the “New World”, people from the “Old World” began to settle there. But another 500 years before the birth of Columbus, the old Normans from Scandinavia -  the Vikings also found one " piece " of the New World .  They sailed west and discovered Iceland, then Greenland , and then later the U.S. mainland. And did you know that there is a Chinese ...

Since the Russian Tsar Alexander II was not particularly interested in Alaska, the Minister of Foreign Affairs at the time of President Abraham Lincoln advocated for it that the United States buy Alaska from Russia. And so, on 20 March 1867 the area of Alaska was sold to the United States for $ 7.2 million dollars (~200 million current dollars)!

Over the years, gigantic storms that originate in the tropics have killed more people around the world than any other single kind of storm. These storms are known by different terms in different regions. They are called hurricanes when they form over the Atlantic Ocean, Caribbean Sea, Gulf of Mexico, or the eastern Pacific Ocean north of the equator.  The same storms are called typhoons when they form over the western Pacific and tropical cyclones when they occur over the southern Pacific or the Indian Ocean. They all produce sustained winds of 120 km/h (74 mph) and faster. In their earlier stages, when their winds range in speed from 63 to 119 km/h (39 to 73 mph), they are generally called tropical storms. Hurricanes, typhoons, and tropical cyclones receive individual names from the weather offices that forecast them and are the only kind of storms named as they occur. Hurricanes occur over oceans with water that is 27°C (80°F) or warmer in areas where there is also a ...

Do you live in a place where the water is "hard"?   It is easy to tell if you do, because a chalky layer, or scale, will usually build up inside your kettle. This layer is often called lime or limescale . Scientists call it calcium carbonate.  It is left on the inside of the kettle when some types of hard water are boiled. Water becomes hard when it soaks through chalk, limestone or dolomite rocks. These are all relatively soft rocks, some of whose chemicals dissolve in the water. When water is boiled, the dissolved substances change, leaving the solid calcium carbonate behind. In many ways, hard water is a nuisance. When you wash in hard water, it is difficult to work soap into a lather. Instead, the soap makes an unpleasant layer of scum on the surface of the water. Because hard water contains harmful minerals, it can also do harm to hot-water systems. Unless special chemicals are added to the water, scale builds up in the hot-water tanks and pipes just ...

Put two or three pinches of table salt into half a glass of water and stir the water with a spoon. What happens? The salt seems to disappear. In fact, it is still there, but it has dissolved in the water. The salt and water have formed a solution. Each grain of salt is a crystal. This is a group of particles arranged in a regular pattern. Water molecules break the crystals up into individual salt particles, which are too small to be seen. This is why the salt seems to disappear. Most of the earth's surface is covered with a solution. We call this solution sea water. There are many things dissolved in it, but the most common substance is a chemical called sodium chloride. We know it better as table salt. It makes the sea taste salty. You may think the salt has disappeared. But taste the water and you will find the salt is still there. You cannot see it because it has dissolved. Some of our salt comes from the sea. First, sea water is allowed to flow into large shallow pool...

How can you tell a fresh egg from a rotten one?  It's easy. Put them in a bowl of water. The fresh egg will sink but the rotten one will float. Fresh eggs sink because they are denser than water. When an egg goes rotten, gas is made and trapped inside. The gas has a lower density than water and this allows the rotten egg to float. But you can make a fresh egg float by dissolving plenty of salt in the water. The salt makes the water denser than the egg. Now the egg will float, or become buoyant. What is the water is only slightly salty? The egg might float or sink, depending on how salty the water is. The fresh egg is denser than the water and so it sinks. The rotten egg has lots of gas. It is less dense than the fresh egg and so it floats.

Hot water or steam in pipes is a convenient way of moving heat around buildings. This is what some central heating systems do. The water is heated up in a boiler and pumped through pipes to radiators in each room. Heat travels from the water into the metal of the radiators. Moving heat from one object to another in this way is called conduction. Now the heat travels from the radiators to warm the air in the room. It does this in two ways. One is by a movement called convection. The radiator heats the air around it. The heated air rises and cool air rushes in to take its place. The hot air moves along the ceiling away from the radiator pushing cooler air in front of it. This convection current moves down the wall opposite the radiator, along the floor and so back to the radiator again. The other way a radiator works is by sending out waves of heat in the same way as the sun. This is called radiant heat. Hot air from the radiator moves around the room. The heat is gradually lost t...

Have you ever stood outside during a bad storm and seen a sudden flash light up the sky?  That was probably lightning. Lightning is very powerful. The heat from a flash of lightning can burn the ground and even set trees or houses on fire. Do you know what lightning is?  Lightning is a giant spark of electricity in the air. Have you ever noticed tiny sparks when you comb your hair, or when you take off a sweater very quickly in the dark? These are sparks of electricity. They are just like lightning flashes, but much smaller and safer. Our body uses electricity all the time.  Our heart produces tiny amounts of electricity to help it beat properly. Our brain is receiving and sending electrical messages to every part of your body, even when you're asleep. All animals' bodies produce electricity, and some even use it as a weapon.  Have you ever heard of the electric eel?  The electric eel lives mainly in the Amazon and Orinoco rivers of South Ameri...

On most nights of the year, the sky is lit up by our nearest neighbor in space, the moon. The Latin word for the moon is “Luna”.  The word lunar means anything to do with the moon. The moon travels around the earth in just over 27 days. Have you noticed that the moon seems to change shape as the month goes by?  The moon does not give out its own light, but we can see it because it reflects sunlight. It also moves around the sun and, as it does, the sun's light falls on part of its surface. The shape we see depends on how much of the moon's surface that faces us is lit up by the sun. The changing shapes are called phases. The moon has a much weaker gravity, or pull, than the earth. Because of this, it cannot hold on to any gases to make up an atmosphere. Where there is no atmosphere, there can be no sound and no weather. Phases of the moon The moon's phases are caused by the position of the moon in relation to the sun and earth. When the moon is between ...