To begin with, there are many kinds of dessert. Some are familiar deserts of bare rock and shifting sand, upon which the hot sun beats down. But some deserts, such as Gobi, have bitterly cols winters. So a desert is really a region where only special forms of life is the kind that has managed to adapt itself to the particular conditions of the particular deserts.
Fr example, cacti are well-known desert plants. They have thick, fleshy stems without true leaves. Desert shrubs that have leaves usually have small ones. Little or no leaf surface prevents too much evaporation of water from the plant.
Many desert plants have thorns, spines or a disagreeable taste or smell. This encourages animals that might eat them and so helps them survive. Desert plants usually lie dormant during the dry or cool season, or drop seeds that can survive such a period.
When the period for growth arrives, the seeds germinate and give rise to plants that rapidly flower and drop more seeds. Within a few weeks or months, the plants are ready again for the long season of dormancy.
When it comes to animals, they must be able to do without water for long periods, or be able to reach water holes at great distances. The camel, for example, is highly adapted to desert life. It has padded feet to walk on sand, a water-storing stomach, humps of fat as a reserve supply of energy, and nostrils that can be closed to keep out of sand during windstorms.
Many of the smaller desert creatures need to drink no water at all. They get what liquid they need from the sap of food plants and from night dew on leaves or stones.
Saturday 16 July 2011
Friday 15 July 2011
What is STONEHENGE?
When we try to learn to accomplishments of ancient man. we usually have to search or dig for evidence. But there is a case where ancient man has left all the evidence standing in a huge structure, and we still cannot understand what it is, what it was used for, and who built it !
This is Stonehenge. It consists of large, standing stones in a circular setting, surrounded by an earthwork, and located near Salisbury, England. As long as the year 1136, it was written that the stones were magically transported from Ireland by Merlin. Of course, this was only a legend. More recently, it was believed that Stonehenge was put up by the Druids, who were priests in ancient Britain. But there is actually no reason to believe that this is so.
Stonehenge has a somewhat complicated structure. On the outside is a circular ditch, with an entrance gasp. Then there is a bank of earth. Inside the bank is a ring of 56 pits. Between these and the stones in the centre, are two more rings of pits.
The stone setting consists of two circles and two horseshoes of upright stones. Then there are separate stones which have been given names, such as the Altar stone, the Slaughter stone, two Stations stones, and the Hele stone.
In most of the holes that have been excavated, cremated human bones have been found. By studying the pottery and objects found, and by making radioactive-carbon tests, it has been estimated that parts of Stonehenge date back to about 1848 B.C., and possibly 275 years earlier or later than this date.
Part of Stonehenge is aligned so that the rising sun in midsummer is seen at a certain point, but nobody is sure is this was intentional.
So this huge and remarkable structure, which may be 4,000 years old, still remains fascinating mystery !
This is Stonehenge. It consists of large, standing stones in a circular setting, surrounded by an earthwork, and located near Salisbury, England. As long as the year 1136, it was written that the stones were magically transported from Ireland by Merlin. Of course, this was only a legend. More recently, it was believed that Stonehenge was put up by the Druids, who were priests in ancient Britain. But there is actually no reason to believe that this is so.
Stonehenge has a somewhat complicated structure. On the outside is a circular ditch, with an entrance gasp. Then there is a bank of earth. Inside the bank is a ring of 56 pits. Between these and the stones in the centre, are two more rings of pits.
The stone setting consists of two circles and two horseshoes of upright stones. Then there are separate stones which have been given names, such as the Altar stone, the Slaughter stone, two Stations stones, and the Hele stone.
In most of the holes that have been excavated, cremated human bones have been found. By studying the pottery and objects found, and by making radioactive-carbon tests, it has been estimated that parts of Stonehenge date back to about 1848 B.C., and possibly 275 years earlier or later than this date.
Part of Stonehenge is aligned so that the rising sun in midsummer is seen at a certain point, but nobody is sure is this was intentional.
So this huge and remarkable structure, which may be 4,000 years old, still remains fascinating mystery !
Thursday 14 July 2011
Whoa. Snow !
Snow is really nothing more than frozen water. Then why doesn't it look like ice?
There are a large number of ice crystals in each snowflake, and the reflection of light from all the surfaces of the crystals makes it look white.
Snow begins to be formed that are clear and transparent. Since there are currents in the air, these tiny crystals are carried up and down in the atmosphere. They fall and rise as different air currents move them along.
While this is happening, the crystals begin to gather around a nucleus, so that in time there may be hundred or more gathered together. When, this group of ice crystals is big enough, it floats down towards the ground. We call this collection of ice crystals a "snowflake". Some crystals are flat and some are like a column of needles. But regardless of shape, snow crystals are always have six sides or angles. The branches of any single snowflake are always identical, but the arrangement of the branches is different in every case. No two snowflakes are ever exactly very alike.
Did you know that snow is not always white ? In many parts of the world red, green, blue, and even black snow have been seen ! The reason for different colours is that sometimes there are tiny fungi in the air, or dust is floating about, and this is collected by the snow as it falls.
There are a large number of ice crystals in each snowflake, and the reflection of light from all the surfaces of the crystals makes it look white.
Snow begins to be formed that are clear and transparent. Since there are currents in the air, these tiny crystals are carried up and down in the atmosphere. They fall and rise as different air currents move them along.
While this is happening, the crystals begin to gather around a nucleus, so that in time there may be hundred or more gathered together. When, this group of ice crystals is big enough, it floats down towards the ground. We call this collection of ice crystals a "snowflake". Some crystals are flat and some are like a column of needles. But regardless of shape, snow crystals are always have six sides or angles. The branches of any single snowflake are always identical, but the arrangement of the branches is different in every case. No two snowflakes are ever exactly very alike.
Did you know that snow is not always white ? In many parts of the world red, green, blue, and even black snow have been seen ! The reason for different colours is that sometimes there are tiny fungi in the air, or dust is floating about, and this is collected by the snow as it falls.
MONSOON?
The word "monsoon" comes from an Arab word means "season". It has to do with a type of climate in which winds blows from the sea to land ( onshore ) during the warm season, and from land to sea ( offshore ) during the cool season. The warm season of onshore winds is often very rainy, while the cool season of offshore winds may be dry.
What cause this seasonal change in winds and rainfall ? It is due to the fact that large continents or land masses heat and cool more rapidly than the surrounding oceans. Central and Southern Asia grow warm rapidly in the spring, and during the summer they are much warmer than the Indian Ocean on the South, or the Pacific Ocean on the east.
The warmer temperatures inland create lower atmospheric pressure, and therefore the wind blows inland from the surrounding seas. This is the onshore or summer monsoon.
In the autumn, interior Asia cools rapidly and during the winter it has much lower temperatures than the surrounding oceans. These lower temperatures create high atmospheric pressure, and therefore the winter monsoon winds blow outward from the dry interior regions toward the sea.
What cause this seasonal change in winds and rainfall ? It is due to the fact that large continents or land masses heat and cool more rapidly than the surrounding oceans. Central and Southern Asia grow warm rapidly in the spring, and during the summer they are much warmer than the Indian Ocean on the South, or the Pacific Ocean on the east.
The warmer temperatures inland create lower atmospheric pressure, and therefore the wind blows inland from the surrounding seas. This is the onshore or summer monsoon.
In the autumn, interior Asia cools rapidly and during the winter it has much lower temperatures than the surrounding oceans. These lower temperatures create high atmospheric pressure, and therefore the winter monsoon winds blow outward from the dry interior regions toward the sea.
What makes stars sunshine?
A star is a ball of very hot gas which shines by its own light. Planets, as you know, and our moon too, shine by light reflected by the sun. And planets shine with a steady light while stars appear to twinkle. This is caused by substances in the air between the star and the earth. The unsteady air bends the light from the star, and then it seems to twinkle.
Why does our sun shine? BECAUSE IT IS A STAR ! And not a very big or bright star at that. Compered to all the other stars in the sky, it might be consider medium-sized and medium-bright. There are millions of stars that are smaller than our sun. Many stars are several hundred times larger than the sun. They all look small because they are so far away.
Ever since the days of the Greek astronomers, some 2,000 years ago, the stars g\have been divided into classes according to their "magnitude", or brightness. Another way of grouping stars is according to their spectra, or the kind of light that comes from the stars. By studying the differences in the spectra, the astronomer may learn about the colours, the temperature, and even the chemical composition of the stars.
Why does our sun shine? BECAUSE IT IS A STAR ! And not a very big or bright star at that. Compered to all the other stars in the sky, it might be consider medium-sized and medium-bright. There are millions of stars that are smaller than our sun. Many stars are several hundred times larger than the sun. They all look small because they are so far away.
Ever since the days of the Greek astronomers, some 2,000 years ago, the stars g\have been divided into classes according to their "magnitude", or brightness. Another way of grouping stars is according to their spectra, or the kind of light that comes from the stars. By studying the differences in the spectra, the astronomer may learn about the colours, the temperature, and even the chemical composition of the stars.
Ou. Solar System !
A solar system is simply a sun and all the bodies around it that it controls by gravity. Out solar system is made up of all the planets, moons, asteroids, and comets that our sun controls by gravity. Out earth is simply one of the planets.
The planets vary greatly in size and distance from the sun. Mercury is the smallest planet and the nearest to the sun. It goes around the sun in only 88 days. Venus is about 68 million miles from the sun, and goes around it 225 days. The earth is 93 million miles from the sun. Mars is about 142 million miles from the sun and goes around it in 687 days.
Jupiter, which is about 483 million miles away from the sun, takes 12 years to make one trip around it. Saturn, 886 million miles form the sun, takes 29 1/2 years to make one orbit. Neptune takes 165 years. so you see, while these planets are part of out solar system, each one is quite different and exist under very different conditions.
What is Virus ?
Virus are very small particles which may cause disease in man, animals, and plants. The words "particles" seems a stranger way to describe them, so let's see why it used.
Virus are so small, they will pass through the finest filters. They cannot be grown in sugar solutions, but will grow and multiply in the presence of living tissue. They are parasites and depend completely upon their host. Viruses are too small to be seen by ordinary microscopes - they have to be photographed through electron microscope.
Viruses cause many diseases with which we are familiar. In attacking organs of the body, each group of viruses causes a different group of diseases. Some of the diseases caused by virus that attack the skin are chicken pox, smallpox, measles, German measles and fever blisters.
Other viruses cause diseases of nerve tissue, such as rabies, brain fever and infantile paralysis. A third group of viruses cause diseases in the internal organs. Yellow fever, influenza, the common cold and viral liver inflammation are examples of this group.
How Does a Volcano form?
In February, 1943, in the middle of a cornfield in Mexico, people saw a rare and amazing thing taking place. A volcano was being born ! In three months it had formed a cone about 300 metres high. Two towns were destroyed and a wide area damaged by the falling ash and cinders.
What makes a volcano form? The temperature under the earth becomes higher and deeper you go. At a depth of about 20 miles, it is hot enough to melt most rocks.
When rocks melts, it expands and needs more space. In certain areas of the world, mountains are being uplifted. The pressure becomes less under these rising mountains ranges, and a reservoir of melted rock ( called "magma" ) may form under them.
This material rises along cracks formed by the uplift. When the pressure in the reservoir is greater than the roof of rock over it, it bursts fourth as a volcano.
In eruption, hot gaseous liquid, or solid material blown out. The material piles up around the opening, and a cone-shaped mound is formed. The "crater" is depression at the top of the cone where the opening reaches the surface. The cone is he result of a volcano.
The material coming out of a volcano is mainly gaseous, but large quantities of "lave" and solid particles that look like cinders and ash are also thrown out.
Actually, lava is magma that have been thrown up by the volcano. When the magma comes near the surface, the temperature and the pressure drop, and a physical and chemical change takes place that changes the magma to lava.
What makes a volcano form? The temperature under the earth becomes higher and deeper you go. At a depth of about 20 miles, it is hot enough to melt most rocks.
When rocks melts, it expands and needs more space. In certain areas of the world, mountains are being uplifted. The pressure becomes less under these rising mountains ranges, and a reservoir of melted rock ( called "magma" ) may form under them.
This material rises along cracks formed by the uplift. When the pressure in the reservoir is greater than the roof of rock over it, it bursts fourth as a volcano.
In eruption, hot gaseous liquid, or solid material blown out. The material piles up around the opening, and a cone-shaped mound is formed. The "crater" is depression at the top of the cone where the opening reaches the surface. The cone is he result of a volcano.
The material coming out of a volcano is mainly gaseous, but large quantities of "lave" and solid particles that look like cinders and ash are also thrown out.
Actually, lava is magma that have been thrown up by the volcano. When the magma comes near the surface, the temperature and the pressure drop, and a physical and chemical change takes place that changes the magma to lava.
Carbon.
Carbon is important to all forms of life. It makes up less than 1 percent of all matter, but everything that lives or has lived contains this element. The bodies of all living things are made up of compounds containing carbon, and where it found in any quantity in the earth, life has probably existed.
Plants get carbon from carbon dioxide gas of the air and use it in building up their roots, stems, and leaves. Animals get it for food from plants. At the same time, carbon dioxide is being returned to the air by animals when they breathe, and by plants when they decay.
Of all the forms of carbon, the best-known, and perhaps the most valuable to man, is coal. Coal is about four-fifths carbon, the rest being hydrogen and other elements. The attraction between carbon and oxygen is almost like that between a magnet and iron.
This is one of the reasons why coal is so valuable. When coal is put into fire, its element, particularly its carbon, burn or combine with the oxygen in the air. This burning produces heat energy, which used by man in many ways.
Carbon atoms can attach themselves to each other and to the atoms of other elements. They combine in many different ways to from many carbon compounds. One of the simplest one is carbon dioxide, which given off into the atmosphere when carbon burns in oxygen. Carbon monoxide, a poisonous gas, forms when carbon burns where there is not enough oxygen.
Plants get carbon from carbon dioxide gas of the air and use it in building up their roots, stems, and leaves. Animals get it for food from plants. At the same time, carbon dioxide is being returned to the air by animals when they breathe, and by plants when they decay.
Of all the forms of carbon, the best-known, and perhaps the most valuable to man, is coal. Coal is about four-fifths carbon, the rest being hydrogen and other elements. The attraction between carbon and oxygen is almost like that between a magnet and iron.
This is one of the reasons why coal is so valuable. When coal is put into fire, its element, particularly its carbon, burn or combine with the oxygen in the air. This burning produces heat energy, which used by man in many ways.
Carbon atoms can attach themselves to each other and to the atoms of other elements. They combine in many different ways to from many carbon compounds. One of the simplest one is carbon dioxide, which given off into the atmosphere when carbon burns in oxygen. Carbon monoxide, a poisonous gas, forms when carbon burns where there is not enough oxygen.
Noise.
Sound is the result of vibrations. Vibration is simply moving back and fourth of some object. When the vibration is very regular, when the sounding body sends out waves at absolutely regular intervals, the result is a musical sound. If the vibration is not regular, the effect on your ears is not all pleasing. The resulting sound is "noise".
The three differences between one sound and another are loudness, pitch, and tonal quality. Loudness of a sound depends partly on the distance from the object to the ear and partly on the amplitude of vibration of the sound-making object. Amplitude means the distance the vibrating body moves in its to-and-fro motion. The greater the movement is, the louder the sound will be.
The highness or lowness of a sound is called its "pitch". Pitch depends on the speed of vibration or the sounding object. The greater the number of vibrations that reach the ear every second, the higher will be the pitch.
The three differences between one sound and another are loudness, pitch, and tonal quality. Loudness of a sound depends partly on the distance from the object to the ear and partly on the amplitude of vibration of the sound-making object. Amplitude means the distance the vibrating body moves in its to-and-fro motion. The greater the movement is, the louder the sound will be.
The highness or lowness of a sound is called its "pitch". Pitch depends on the speed of vibration or the sounding object. The greater the number of vibrations that reach the ear every second, the higher will be the pitch.
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