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Our Solar System

Our solar system comprises the sun and eight known planets which orbit around it. The solar system also consists of:

  • The Natural satellites accompanying the Planets
  • Several thousand minor planets called asteroids
  • A Large number of comets

Solar System and Planets

The Planets

The Bodies revolving around the sun (at the same time rotating on their own axis) are called planets. There are eight known planets:

Mercury: It is the planet closed 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 also the fastest planet in our solar system.

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

Earth: The earth is in the third position from the sun and is the fifth largest planet in the solar system.

Mars: It is the fourth planet from the sun and is next after the earth. It is also known as the red planet. Because of its similarities with earth, astronomers have been speculating on the existence of some kind of life on this planet.

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

Saturn: It is the outermost planet visible to the naked eye and second largest in size after Jupiter. The most spectacular feature of Saturn is its system of rings.

Uranus: It is the seventh planet from the sun and is not visible to the naked eye. It was discovered in 1781 by William Herschel.

Neptune: It is the eighth in position from the sun. It was discovered by J. G. Galle in 1846.

Which is farthest, Neptune or Pluto?

Pluto revolves farther from the sun than any of the planets for most or its orbit. However, because of its orbital eccentricity, Pluto moves closer to sun for approximately 20 years, leaving Neptune at a farther distance. From January 23, 1979 Pluto moved closer to the sun and remained in that position till March 15, 1999. After 1999 it is now Pluto?s turn to go further and Neptune will remain closer to the sun for approximately 228 years.


Satellites are bodies which revolve around the planets. There are approximately 153 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

Important Data on the Moon

  • Distance from earth (centre to centre) -3.84,400 km
  • Distance from the earth (surface to surface)-3,76,284 km
  • Diameter (Period of option units axis 28 days)-3475 km
  • Orbital Speed- 3680 km/s
  • Period of rotation on its axis-28 days

The Moon

The Moon is earth?s natural satellite and is its nearest neighbor in space. It revolves around the earth while rotating on its own axis. The moon is about 1/6th the size of the earth. The moon takes 27 days, 7 hrs, 43 min and 11.47 sacs to complete one revolution of the earth. It rotates on its axis in exactly the same time. Hence, we see only one side of the 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 July 21, 1969 when they first set foot on the moon.


It is believed that asteroids are debris left over from the formation of the inner planets. They are too small to retain any atmosphere of their own. Asteroids are also called ?planetoids? or small planets. They circle around the sun between the orbits of Mars and Jupiter. There are about 50,000 known asteroids in our solar system. The largest is Ceres with a diameter of 1025 km.


Meteors are small bodies often seen in the sky, shooting with great speed from one point to another and producing a trail of light. Meteors may burn up or fall on earth (known as shooting stars) in the form of dust or fragments (called meteorites).


Comets are celestial bodies that move around the sun. A Prominent feature of a comet is its long tail, and hence, its name, which comes from the Greek, word Kometes, Meaning ?hair-like?. Some important comets are; Halley?s D?Arrest, Encke, Borrelly, Pons-winnecke, Finlay, Faye, Smith-tuttle etc.

Important Comets

Helley?s Comet is perhaps the most famous comet, named after the British astronomer, Edmund Halley, who discovered it in 1705. He stated that the comets seen in 1531, 1607 and 1683 were in fact the same body, which circles the sun every 76 years. Halley?s Comet last appeared in 1986 and it may reappear again after 76 years.

Comet ?Smith-Tuttle? is a huge comet heading on a collision course with earth on August 17, 2116. It was first sighted in 1862 and rediscovered in 1992. It could kill off most of life with an explosion more powerful than the explosion of a million nuclear bombs put together.

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