Starfish Facts for Kids - What is a Starfish?

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 inside.
To eat, the starfish pushes its stomach out of its mouth and folds it around the food!
Starfish are not fish and do not have gills to take in oxygen from the seawater.
Instead, they use their tube feet to absorb oxygen from the water.

Jellyfish Facts for Kids - What is a Jellyfish?

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 pull the trapped animal into its mouth.

The tentacles of a jellyfish are covered with tiny capsules.
Inside each capsule is a thorny stinging thread.
The jellyfish whips out these threads to paralyze small animals.


If you see a jellyfish, even one that has been washed up on the beach, don't touch it.
The poison from some jellyfish stings can be deadly to human beings. 

Anyone stung by a sea wasp, a kind of Australian jellyfish, will almost certainly die within a few minutes.

But common jellyfish sting do not kill.

Jellyfish and corals belong to a group of invertebrates called coelenterates.
The term coelenterate means "hollowbody."
Some species of jellyfish produce their young from eggs.
The eggs grow into hollow cylinders, called polyps, which attach themselves to the seabed.
New jellyfish start to grow on these polyps.
Each bud of a mature polyp looks like a tiny saucer.
When a bud is big enough, the polyp releases it into the sea and it grows into an adult jellyfish.

Who Discovered America First - Was it Columbus?

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 folk legend about an even earlier trip, when Chinese sailors discovered today’s California? 
And people from Pacific Ocean islands still sing about famous people from their history, who sailed to South America long before white people arrived to South America and to their island.
As we know , they could be many research era thousands of years ago.
And certainly it was before Columbus.
We could possibly say that neither they nor Columbus, neither Normans had "discovered" America. Native Americans - Indians were living there for centuries before the white man came.
And who can say that they have not arrived in America after such a research endeavor?
It is believed that the Indians came from Asia, but no one knows when and how.
They must have settled over many centuries in different ways.
It is also likely that they first sent their scouts, who were looking for land and sea routes. These people were their explorers, and maybe they really had discovered America!

Alaskan Purchase - When Was Alaska Sold To USA?

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)!

What are Hurricanes - Hurricanes facts for kids

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 layer of humid air that’s a few thousand feet thick.
These storms draw their energy from the warm water and humid air.
During their lives, these storms flow along the paths of the Earth’s large-scale winds, much like twigs floating with the current of a river.
When the storm moves over land or cold water it begins to die, but a storm can stay over a warm ocean for a week or two, sometimes even longer, growing stronger or at least not losing much strength.
A hurricane consists of lines of thunderstorms that spiral into the storm’s calm center, which is called the eye.
Winds grow stronger as you approach the eye, and the very strongest winds occur in the wall of thunderstorms around the eye, called the eye wall.
As a hurricane’s winds blow hour after hour, sometimes faster than 160 km/h (100 mph), water piles up on the ocean surface near the hurricane’s center. If the storm hits land it brings with it this mound of water, called a storm surge, which can be up to 6 m (20 ft) high. Until 1969 storm surges accounted for most of the hurricane-related deaths in the United States.
Since then, better forecasts and well-organized evacuations have moved people out of the way of storm surges when hurricanes threaten, saving hundreds of lives.
From 1970 through 2000 storm surges killed only half a dozen people in the United States.
Since the 1970s the big killers in hurricanes have been floods on inland rivers and streams caused by the drenching rain that even a weak hurricane brings.
Storm surges still present a real danger for those who don’t evacuate, of course. While water kills most hurricane victims, a hurricane’s wind, which can blow faster than 160 km/h, is also dangerous; it accounts for many deaths and causes a great deal of destruction.

How to Soften Hard Water?

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 as it does inside a kettle. In time, the hot-water pipes may become blocked.

How to soften hard water?

One simple way of making hard water softer is to add a small amount of washing soda.
The chemical name for washing soda is sodium carbonate.
It removes the minerals that make the water hard. This stops a film of scum from forming and allows lather to form in the water when soap is added.
One simple way of making hard water softer is to add a small amount of washing soda.
The chemical name for washing soda is sodium carbonate.
It removes the minerals that make the water hard.
This stops a film of scum from forming and allows lather to form in the water when soap is added.

How to test for hard water - Home test

Find out if you live in a hard or soft water area.
You will need:
a bowl of water soap
washing soda a spoon
1. Run some water into the bowl and wash your hands using soap.
Did it make plenty of lather quickly? 
If so, your water supply is soft.
2. If the soap left a film of scum on your hands instead of working into a lather, empty and rinse the bowl and refill it.
Add one spoonful of washing soda and stir with the spoon until it dissolves.
Now take the soap and wash your hands again.

Why is the Sea Salty?

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 pools.
The heat of the sun evaporates the water, leaving the salt behind.
Substances which dissolve in water are described as soluble substances.
We can make soluble substances dissolve faster by stirring, shaking or warming them.

What would happen if you continued to put more salt into the water? 

After a time, no more would dissolve, however much you stirred it, shook it or warmed it. The solution would be saturated. A saturated solution cannot hold any more of a soluble substance.

Water Test for Eggs - Test Eggs for Freshness

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 more dense 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 more dense 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 more dense 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.

What is the function of platelets in blood?

The smallest cells in the blood are the platelets, which are designed for a single purpose—to begin the process of coagulation, or forming a clot, whenever a blood vessel is broken. 

As soon as an artery or vein is injured, the platelets in the area of the injury begin to clump together and stick to the edges of the cut.
They also release messengers into the blood that perform a variety of functions: constricting the blood vessels to reduce bleeding, attracting more platelets to the area to enlarge the platelet plug, and initiating the work of plasma-based clotting factors, such as fibrinogen.
Through a complex mechanism involving many steps and many clotting factors, the plasma protein fibrinogen is transformed into long, sticky threads of fibrin.
Together, the platelets and the fibrin create an intertwined meshwork that forms a stable clot.
This self-sealing aspect of the blood is crucial to survival.

What is the function of thrombocytes?

Thrombocytes, or platelets, are the smallest cellular component of blood. They circulate inactivated, about 250,000 per cubic mm of blood, until they come into contact with a damaged blood vessel.
At this point, the platelets form a clump, adhering to each other and to the blood vessel wall.
They secrete chemicals that alter a blood-borne protein, fibrinogen, so that it forms a mesh of fibers at the damage site. A clot forms when platelets and red and white blood cells become trapped in the fibers.
Blood clotting begins within seconds of injury.

What is the function of white blood cells?

White blood cells only make up about 1 percent of blood, but their small number belies their immense importance.
White blood cells play a vital role in the body’s immune system—the primary defense mechanism against invading bacteria, viruses, fungi, and parasites. 
They often accomplish this goal through direct attack, which usually involves identifying the invading organism as foreign, attaching to it, and then destroying it. This process is referred to as phagocytosis.
White blood cells also produce antibodies, which are released into the circulating blood to target and attach to foreign organisms. 
After attachment, the antibody may neutralize the organism, or it may elicit help from other immune system cells to destroy the foreign substance.
There are several varieties of white blood cells, including neutrophils, monocytes, and lymphocytes, all of which interact with one another and with plasma proteins and other cell types to form the complex and highly effective immune system.

What is the function of red blood cells?

Erythrocytes, or red blood cells, are the primary carriers of oxygen to the cells and tissues of the body. 
The biconcave shape of the erythrocyte is an adaptation for maximizing the surface area across which oxygen is exchanged for carbon dioxide. Its shape and flexible plasma membrane allow the erythrocyte to penetrate the smallest of capillaries.
Red blood cells make up almost 45 percent of the blood volume. 
Their primary function is to carry oxygen from the lungs to every cell in the body. Red blood cells are composed predominantly of a protein and iron compound, called hemoglobin, that captures oxygen molecules as the blood moves through the lungs, giving blood its red color.
As blood passes through body tissues, hemoglobin then releases the oxygen to cells throughout the body. Red blood cells are so packed with hemoglobin that they lack many components, including a nucleus, found in other cells.
The membrane, or outer layer, of the red blood cell is flexible, like a soap bubble, and is able to bend in many directions without breaking. This is important because the red blood cells must be able to pass through the tiniest blood vessels, the capillaries, to deliver oxygen wherever it is needed.
The capillaries are so narrow that the red blood cells, normally shaped like a disk with a concave top and bottom, must bend and twist to maneuver single file through them.

What is the function of blood?

Blood carries oxygen from the lungs to all the other tissues in the body and, in turn, carries waste products, predominantly carbon dioxide, back to the lungs where they are released into the air.
If oxygen transport fails, a person dies within a few minutes.
When oxygen transport fails, a person dies within a few minutes. Food that has been processed by the digestive system into smaller components such as proteins, fats, and carbohydrates is also delivered to the tissues by the blood. These nutrients provide the materials and energy needed by individual cells for metabolism, or the performance of cellular function.
Waste products produced during metabolism, such as urea and uric acid, are carried by the blood to the kidneys, where they are transferred from the blood into urine and eliminated from the body. 
In addition to oxygen and nutrients, blood also transports special chemicals, called hormones, that regulate certain body functions. The movement of these chemicals enables one organ to control the function of another even though the two organs may be located far apart.
In this way, the blood acts not just as a means of transportation but also as a communications system.
The blood is more than a pipeline for nutrients and information; it is also responsible for the activities of the immune system, helping fend off infection and fight disease. 
In addition, blood carries the means for stopping itself from leaking out of the body after an injury. The blood does this by carrying special cells and proteins, known as the coagulation system, that start to form clots within a matter of seconds after injury.
Blood is vital to maintaining a stable body temperature; in humans, body temperature normally fluctuates within a degree of 37.0° C (98.6° F). 
Heat production and heat loss in various parts of the body are balanced out by heat transfer via the bloodstream. This is accomplished by varying the diameter of blood vessels in the skin. When a person becomes overheated, the vessels dilate and an increased volume of blood flows through the skin. Heat dissipates through the skin, effectively lowering the body temperature. The increased flow of blood in the skin makes the skin appear pink or flushed. When a person is cold, the skin may become pale as the vessels narrow, diverting blood from the skin and reducing heat loss.

What is Hot Water Heating?

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 to the cool air by conduction.
What is Underground Water?

What is Underground Water?

Everything on the earth, including water, is affected by the force of gravity. 
In trying to pull water down towards the center of the earth, gravity pulls water into the ground. As water meets soil and rock, some soils let water soak through them. 
They are called porous soils. Non-porous soils do not let water pass through.What happens when rain water soaks into the ground? 
Soil is usually porous. So are some kinds of rock. 
Other kinds of rock are non-porous. 
Some types of soil are barely porous. 
Gravity makes rain water soak into most soils and also into porous rock. Once the soil and rock have become full of water, they cannot soak up any more water. 
They let the water pass through until it reaches non-porous rock. 
Then it can go no farther. 
The water gathers in the spaces between the rocks as groundwater.
All over the world there are great stores of groundwater. 
This sometimes escapes through holes in the surface to make a spring. 
Or else we can dig a well to reach it.

What Are The Building Blocks of Matter?

The world is made up of all sorts of things.
Just look around you.
There are houses, cars, trees, and people.
All these things are different shapes, sizes, and colors.
Look closely at some of them.
They are made from different materials.
Some are hard and cold. Others are soft and warm. They may be wet or dry, rough or smooth.
All these things look and feel different to us.
The different things in the world have two things in common. They are all made of something, which means they have substance, and they all take up space.
Anything which takes up space is called matter. 
So a pencil, a book, a house, a tree, the air, and everything around you is matter. You are matter, too. The whole earth is matter, and so are the stars throughout the universe and the dust that drifts between them.
Imagine you are using a knife to divide a drop of water or a grain of sand. You can divide them again and again, until the pieces are so small that you can no longer see them. Scientists can divide these tiny particles of matter even smaller under a powerful microscope. They divide them again and again, until the particles are so small that they can no longer be seen clearly, even under the microscope. Whatever in the end makes up matter is so small that we cannot see it.
But everything in the world—animal, vegetable, mineral, solids, liquids, and gases—is made of matter.

Space and energy

Because space has no substance and obviously does not take up space, it does not qualify as matter. Neither does energy, which is the ability to do work.
However, matter and energy are not completely separate. Many scientists believe that matter and energy are two aspects of the same thing, like liquid water and ice are two aspects of water.

The building blocks of matter

Have you ever played with building blocks?
The blocks can be joined together to make all kinds of things.
Scientists think this is how the world is made up. Tiny particles join together, like building blocks, to make up matter. 
The matter in the universe is made from tiny particles called atoms. Millions and millions of atoms combine to make the different things around us—even the air we breathe.
Atoms are the building blocks of matter.
Atoms are so small that they can't be seen. But scientists can take photographs of atoms using electron microscopes. With the help of these photographs, scientists can describe what atoms are like and build models to show how they behave.

Imagine that an atom is like a tiny solar system. In the center of the atom, there is a part called the nucleus.
The nucleus contains particles called protons and neutrons.
Whirling around the nucleus are much smaller, lighter particles called electrons, always in motion. You can think of the nucleus as the sun, and the electrons as the earth and other planets circling around the sun. 
There is constant motion in matter.
Matter around us is made up of atoms.
But there is more than one type of atom. In fact, there are over one hundred different types, which make up the elements.
Elements are substances which are made up of many of the same type of atom. The metal called iron is an element made up of iron atoms.
The gas called hydrogen is an element normally made up of pairs of hydrogen atoms.
Elements are the simplest chemical substances.
We don't often deal with atoms. Rather, we deal with the elements.
How can we tell an atom of iron from an atom of hydrogen? 
Each atom is made up of electrons circling around a nucleus. The nucleus is made up of protons and neutrons. An atom of hydrogen has only one proton and one electron. An atom of iron has 26 protons and 26 electrons. The number of neutrons can vary. But hydrogen will always have one proton and one electron, and iron will have 26 protons and 26 electrons. The number of protons determines the element.

Where Does Our Electricity Come From?

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 America. This eel is a fish that makes its own electricity to help in catching food and in protecting itself against enemies.
The eel's body can make enough electricity to kill a small fish or to stun a human being.
We don't use electric eels to light up bulbs!
Most of the electricity, or electric current, we use comes from huge power stations.

Can you think of some ways that we use electricity?

  • Electricity lights up bulbs so that we can see at night.
  • Electricity heats up ovens so that we can cook food.
  • Electricity helps to carry our voices along the wires when we speak to people on the telephone.
  • Electric trains quickly take people from one place to another.
  • Electricity makes it possible for computers to do complicated calculations.
  • Electricity lights up the whole of the city at night.

Interesting Facts About the Moon

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 the earth and the sun, we can't see it at all.
We call it the new moon.
About a week later, we see half of it lit up.
This is the first quarter.
About a week later, all of it is lit up and it is the full moon.
 It is half lit up again at the last quarter, about a week later.
It eventually disappears at the next new moon, 29 1/2 days after the previous one.

As the moon changes from new moon to full moon, it is said to be waxing.
During the period from full moon back to new moon, it is said to be waning.
When the moon looks larger than half a full moon, it is called gibbous.

The moon's dimensions

Part of the surface of the moon consists of great, flat plains that are covered in dust.
The rest of the surface is made up of highlands and towering mountain ranges.

Some of the mountains soar to a height of over 23,100 feet (7,000 meters).
Everywhere on the surface there are craters, which are holes made by lumps of rock raining down from outer space.
The smaller craters are just a few inches wide, while others are great depressions or pits up to 700 miles (1,100 kilometers] across.
The moon is about a quarter the size of the earth. 
It measures 2,160 miles (3,476 kilometers) across.
The distance from the earth to the moon is about 238,857 miles (384,403 kilometers). 
We never see the far side of the moon from earth.
This is because the moon rotates on its axis in the same time it takes to circle the earth.
But we know what the far side of the moon looks like from photographs taken by satellites in space or by astronauts in their spacecraft.