General Knowledge and Current Affairs September 2017

Solar System and its Eight Planets

Our solar system comprises the sun and eight known planets which orbit around it.
The solar system also comprises of :
# The natural satellites accompanying the planets.
# Several thousand minor planets called asteroids.
# A large number of comets.

The Planets :

The bodies revolving around the sun but at the same time revolving around its own axis is called planets.
There are eight known planets


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Mercury : First Planet in Solar System

Mercury : It is the planet closest to the sun. It rotates on its own axis in 58.65 days and takes 88 days to complete one revolution around the sun. Thus, it is called the fastest planet in our solar system.






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Venus: Second Planet in Solar System

Venus : It is the brightest object in the sky after sun and the moon. It is also the hottest planet in our solar system .It rotates backwards on its own axis.






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Earth : Third Planet of Solar System

Earth : The earth is in the third position from the sun and the fifth largest planet in the solar system. The earth is a ball flattened at the pole with slight bulge at the centre (equator). The rotation of earth at high speed has caused its mass to bulge at the equator . The earth is made up of number of concentric layers of material.

Composition	Percentage
Oxygen	46.6
Silicon	27.72
Aluminium	8.13
Iron	5.01
Calcium	3.63
Sodium	2.85
Potassium	2.62
Magnesium	2.09

The earth has four distinct spheres :

Lithosphere : Top crust which include land surface and ocean floor.

Hydrosphere :   Water surface which includes oceans, seas, rivers and lakes.

Atmosphere : The cover of air that envelops the earth’s surface.

Biosphere : The Region where life exists.



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Mars : Fourth Planet in Solar System

Mars : It is the fourth planet in the solar system.  It is also know as red planet. Due to its similarities with earth, astronomer has been speculating existence of life on Mar.



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Jupiter : Fifth planet in Solar system

Jupiter : Jupiter is the largest planet in the solar system. Its diameter is 11 times the diameter of the earth. It has 63 satellites.






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Saturn : Sixth Planet in Solar System

Saturn : It is the outermost planet visible to naked eye and second largest in size after Jupiter.






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Uranus : Seventh Planet in solar system

Uranus : It is the seventh largest plant from the earth and not visible to naked eyes. It was discovered in 1781 by William Herchel .






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Neptune : Eighth Planet in Solar System

Neptune : It is the eighth planet in the solar system. It was discovered by J.G. Galle in 1846.




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Pluto

Pluto : From its discovery in 1930 till 2006 , it was considered the ninth and smallest planet.  However, on 24 August 2006, the International Astronomical Union has reclassified Pluto as dwarf planet . Therefore , we now have only eight planets in our solar system.



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Satellites

Satellites : Satellites are bodies that evolve around the planets. There are approximately 180 satellites in our solar system.

Planet	No of satellites
Mercury	0
Venus	0
Earth	1
Mars	2
Jupiter	63
Saturn	47
Uranus	27
Neptune	13

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The Moon

The Moon :

The Moon is earth’s natural satellite and is its nearest neighbor in space.It revolves round the sun while revolving round the earth. The moon is 1/6 of size of earth. The moon takes 27 days, 7 hrs, 43 min to complete one revolution of earth. It rotates on its axis in exactly the same time. Hence, we see  only one side of moon. The moon is the first member of our solar system to have been visited by man. Neil Armstrong and Edwin Aldrin created history on 21 July 1969 when the first stepped on Moon.


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Asteroids

Asteroids : Small planets formed by debris left over from the formation of inner planets. Asteroids are also called as Planetoids  They circle around the sun between orbit of Mars and Jupiter.






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Comets

Comets : Comets are celestial bodies that move around the sun.

Important Comets:

Halley’s comet  known after its British astronomer, Edmund Halley,who discovered it in 1705. He stated that the comets seen in 1531, 1607 and 1683 were the body which circles the sun in every 76 years.

Comet ‘Smith Tuttle’ is a huge comet heading on a collision with the earth on 17 August 2116. It was first sighted in 1862 and rediscovered in 1992 .It could kill most form of life with explosion more powerful than the explosion of several necular bombs put together.


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