Our earth and universe

Our earth

Our earth is only a small speck in huge universe. In this very huge universe, only the sun and the stars give out light and heat. Both the earth and the moon have no light of their own. 

They only reflect the ravs of the sun. The sun is the centre of the Solar System. It is the only source of energy (light and heat) for the planets. Planets are such objects which give out on light of their own. a. The Chief Planets of the Solar System: The chief planets are 
1. Mercury 
2. Venus 
3. Earth 
4. Mars 
 5. Jupiter 
6. Saturn 
7. Uranus 
8. Neptune 
9.Pluto 
 The planets nearer the sun are hotter than those that are far off. Mercury and Venus are so hot that no life can exist on them. Our earth, however, receives just the right amount of heat for the development of vegetation, animal and human life. The Viking Spacecraft sent to Mars has proved that the planet is too cold for any kind of life. 
The remaining outer planets are still farther away for life. Of all the planets, the earth is the only one where different kinds of life can thrive Asteroids: Besides the sun and the nine planets, our Solar System also consists of the ring of countless asteroids or tiny planet. So our Solar System consists of nine big planets revolving round the sun and the ring of countless asteroids.
 There should be certain physical conditions for existing life anywhere We know only one kind of life that exists on the earth. There are some necessary conditions for this life too. The most important is the temperature It should, he neither too hot nor too cold. 
Since our earth receives just the right amount of heat from the sun for the development of vegetation, animal and human, thereby there is life on earth. Moreover earth-has water and oxygen for plants and animats which is necessary for life. The all other plants that we know are extremely hot or extremely.Therefore life is absolutely impossible on them. 
For example, the Viking spacecraft sent to Mars has proved that the is too cold for any kind of life. In short, life needs suitable physical condition temperature which are available only, on earth about two thousand millions years ago our Solar System cad existence as a result of stellar encounter. Millions of the stars move ii universe. They travel in complete isolation. 
Two thousand million years ad star in space came close to our sun. It raised huge tides of boiling matter! surface of the sun. Then this tide assumed the shape of a big mountain mountain rose higher and higher. It travelled over the surface of the’.sum direction of the star, because the star was pulling it. 
Then this mountain separated from the sun. It was divided into fragments. Before it, these pij fragment touched the pulling star, it moved away. So these pieces bJ circulate round the sun. They were called planets. Our earth is one of them. 1 This means the earth and the planets are the result of a star comil the sun. There planets were very hot in the beginning. 
As time passed by, tin their heat and cooled down. Our earth was also very hot in the beginning] cooled down and life was born on it. Satellites: Some portions of the planets broke away from them and started] round the sun. They were called satellites. In this way our Solar System, came into existence along with its nin] planets, countless asteroids and many comets etc. When the earth broke away from the sun, it was intensely hot.
 As time pass surface cooled down. But the interior of the earth is still very hot. According estimate; the temperature goes up by about degrees centigrade for even metres of depth below the surface. Moreover, the lower you go, the greater pressure of the rocks above. On the basis ,of temperature, pressure 
 of rocks found, the interior of the earth may be divided into three parts. 
The centre or the core of the earth is so hot and is under such] pressure that every bit of it feels solid. There are heavy rocks of nickel and The outer rim of the core is under less pressure. The rocks here are in a On top of the core, there is the middle part of the earth’s interior which is the thickest of the three parts. 
The rocks found here are lighter than those of nickel and iron and are brownish in 'colour. 
On top of the middle part, there is the crust of the earth. It. contains only light rocks. The core or centre of the earth is extremely hot due to the great pressure of the earth from the top layers. It has been estimated that the temperature goes up by 12°C for every hundred meter of the'depth below it. Moreover, the lower we go the greater is the pressure of the rocks above it. This is due to great pressure on the centre of earth, the core of the earth is terribly hot. As the surface of the earth gradually cooled down,. the planet passed through a period of dramatic changes and the following things were formed: 
 When the surface of the earth began to cool, disturbances in the earth’s interior caused the crumbling and cracking of the crust. This led to the formation of upfolds or fold-mountains and the downfolds or deep depressions. The cooling of the surface led to profuse evaporation and torrential rains.
The rain-water pouring an the upfolds started running downward and rivers came into being. The deep depressions got filled with, water and became the seas and the oceans. After the new moon, we see a greater part of the moon lit up night after night. On the seventh night it becomes the half moon and on the fourteenth night it shines majestically as the full moon.
 From then on, the bright face of the moon starts diminishing. It starts rising a little later each night but keeps shining till morning. On the 21st night it is once again the half moon. The process of diminution continues. A night before the new moon, no moon appears in the sky. As we already know that the moon revolves round the earth and the sun. 

Eclips of sun

The earth and the moon have no light of their own and both receive their light from the sun. The surfaces of both the earth and the moon are made up of solid rocks through which rays of light cannot pass. We have seen that at new moon, the moon moves directly between the sun and the earth. The sun disappears behind the moon and we have an eclipse of the sun. 
The eclipse can be seen only on parts of the earth from which the sunlight has been cut off. If all sunlight is cut off at a place, the entire disc of the sun becomes dull. Such a place has a total eclipse of the sun. 

Why we do not have a total eclipse of the sun every time when there is a new moon? 

 The moon’s orbit is elliptical and is inclined at an angle of 5 degrees to the plane of the earth’s orbit. That explains why we do not have a total eclipse of the sun every time when there is a new moon. 

Eclips of moon  and new moon

The moon revolves both round the earth and the sun and the moon completes its circuit round the earth in about 28 days. The different phases of the moon are the result of its position in respect to the earth and the sun. At new moon, it is between the earth and the sun and all the three bodies ar almost in a straight line. 
At full moon, it is the earth that comes directly between the sun and the moon. Sunlight to the moon or to a part of it may be shut off by the earth and we have an eclipse of the moon.

 Why we do not have an eclipse of the moon at every full moon? 

Just as we do not have an eclipse of the sun at every new moon, for the same reason we do not have an eclipse of the moon at every full moon. 

The great bear  milky way

 The starry sky on a clear night is always a wonderful sight. Some of its features easily attract the attention of most of us. One of these is the constellation of seven bright stars known as the Great Bear. The other one is the broad faint band of light across the sky. This is known- as the Milky Way.