Geography

Origin of Universe –  

universe — 15 -20 billion year old

earth — 4– 5 billion year old

human being evolved – 2 million year old

Earth is one of the eight planet orbiting around the sun. Sun is about 150 million KM far from earth. Earth, other planets, stars (galaxies) form the universe.




There are also countless asteroids & comets in orbit around  the sun. it may be seen by telescope.

Planets distance from Sun-

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Difference Between Asteroids & Comets –

Asteroids are rockier and more metallic while comets tend to be icer. Both asteroids  & comets are made during earliest  history of solar system,  around 4.5 billion years ago, Asteroids are near the sun so it is much hot while comets  are far from the sun so it is iced but when it is near the sun it forms a tail like structure due to vaporization  of its comets.  While such vaporization is very rare in asteroids. Another difference is comets is very extended & elongated while asteroids are small & circular in structure.

Origin of the universe & origin of earth –

1–Big bang theory is most accepted. According to this theory universe  started with a huge explosion and matter( dust & gases ) filled the entire space. Temperature that time was about 100 billion degree celcious

2–It is believed that this big bang occurred about 15 -20 billion years ago the huge collection of dust & gases then began to spin. As it spun faster faster became very hot. It become sun & from the edges chunk of dust broke out & form 8 ball shaped planets & finally solar system occurred.

3-Earth broke out about 4.5 billion years ago with an explosion. It was a burning hot white mass of gas & dust over a long period of time. Dust & Gases gradually condensed & solid rock occurred due to condensation and shrinking it become very hot. As result rock melted into a gluey liquid. After million of year ago the outer surface cooled & again formed a hard rock just as melted chock-lets.  The interior is very hot still

4. Cooling the earth crust hardens and formed the land. Cooling of the earth also condensed water vapor into liquid water filling the depression formed the sea.

Classification of planets 

1- The eight planets have bee divided into tow groups all the planets of a particular group have some common features terrestrial planets or rocky planets and jovian planets or gaseous planets are the tow groups of planets




2- The four planets nearest to the sun – mercury venus earth and mars are called terestrial planets because their structure is similar to the earth

3- Other four planets —jupiter, saturn  uranus and neptune are called jovian planets

4- Planets are classified into the following tow groups inner and outer planets these are separated by asteroid belt

INNER PLANETS — 

1- The include mercury venus earth mars

2- They are nearer to the sun

3- The are made up of dense metallic minerals

4- They move faster and have a shorter period of revolution

5- They have thin rocky crust

6- They have a mantle rich in iron and made of gases magnesium

7- They have a core of molten metals

8- They have thin atmosphere

9- They have very few natural satellites or no satellites

OUTER PLANETS ;

1- They include jupiter saturn uranus neptune etc

2- They are far away from the sun

3- They are made up of hot gases mainly hydrogen and helium

4- They move rather slowly and have a longer  period of revolution

5- They are all gaseous bodies

6- They have ring systems around them

7- They have a large number of natural satellites

 

1- Universe:

(a)The universe is commonly defined as the totality of everything that exists including all physical matter and energy the planets stars galaxies and the contents of intergalactic space

(b)The study of universe is known as Cosmology .

Cosmology = cosmos   ( universe ) + logos ( science)

(c)The universe has no limit

2- Galaxy:

(a) A galaxy is vast system of billions of staes which also contains a large number of gas clouds and dust isolated in space from similar systems .

(b) The milky way  galaxy is the home of the earth and our solar system it is spiral in shape .

(c) Latest known galaxy is the Dwarf Galaxy .

(d) Origin of the universe is explained by the Big Bang Theory formulated and proposed by the belgian astronomer and cosmologist Georges Lemaitre .

3- The Big Bang Theory;

(a) Big bang was an explosion that occurred  15 billion years ago leading to the formation of galaxies of stars and other heavenly bodies

4- Star:

(a) Stars are made of hot burning gases

(b) Light takes about 4.3 years to reach us from the next nearest star Proxima centauri.

5-The solar system