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Solar System

definition

Solar System

A celestial body should satisfy the following criteria to be labelled as a planet:
1. It orbits around the sun.
2. It has sufficient mass to form a spherical shape.
3. It has a clear neighbourhood around its orbit. 
Solar system is composed of eight planets as shown in the figure. Pluto is considered as a dwarf planet because it fails to satisfy the third criteria. Planets nearer to the sun travel at a faster speed as compared to planets away from the sun. 

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Other members of solar system

Asteroids: Small bodies that revolve around the Sun in between the orbits of Mars and Jupiter.
Comets: Comets revolve around the Sun in highly elliptical orbits and have very long time period of revolution. It appears as a bright head with a long tail always pointing away from the sun. Eg: Halley's Planet.
Meteors (Shooting Stars): Meteors are small bodies that enter the earth's atmosphere. They get heated up and evaporated before reaching the earth's surface due to the air resistance provided by the atmosphere. Meteors that reach earth's surface are called Meteorites.

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Planets of Solar system

Mercury:
Mercury is the nearest planet to the

sun. Sun rises or sets within about two

hours of Mercurys rising or setting. You

can spot it at the place of sunrise or

sunset, early in the morning or soon

after the sunset.Mercury has heavily cratered surface.
Surface temperature varies from   to . Its specific gravity is .Its period of rotation and period ofrevolution are days and days respectively.

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Venus

Venus is the second planet from Sun.It can be recognized easily. Its atmosphere is

made up of mostly carbon dioxide.

Sun rise and Sun set as seen from

the planet will be in the West and

East direction respectively.
Its period of

rotation is 243 days and takes 224

days to go around the sun once. It

means a day on Venus is longer than

its year.

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Earth

Earth is the third planet from the Sun. Earth has one known natural

satellite, the moon. Earth is the only planet in the solar system on which

life is known to exist. Only Earth has atmosphere and nearly 2/3 part of it is covered with water.The layers of atmosphere contain nitrogen, oxygen, carbon dioxide, water vapour and small quantities of other gases.

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Mars

Mars is the fourth planet . It is a reddish planet. Space crafts like Viking have explored Mars, for evidence of life.Some places in mars have moderate range of temperature. It has oxygen, nitrogen and water. It has frozen carbon dioxide near the poles which look like caps.Mars has two natural satellites Phobos and Deimos. The specific gravity of Mars is . The surface temperature varies from less than to .Period of rotation of mars is about  hours. Its period of revolution is days.

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Jupiter

Jupiter is the fifth planet. It is the biggest planet of the solar system. Its Orbital period is nearly 12 years. Its day is about 10 hours. That means it rotates very fast. Due to fast rotation it is bulged at the equator and flattened at the poles. The thick gas clouds which are attached to the planet due to its strong gravitational force also rotate with the planet resulting in bands.These bands are visible through a telescope.Jupiter is having many natural satellites, the largest are Io,Europa, Ganymede and Callisto.Jupiter emits radio signals.

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Saturn

Saturnisthesixthplanet.Itisthesecondbiggestplanet.Itisamostfascinatingexperiencetoviewthisplanetusingatelescope.Its special feature isprominentringsystem.Theringsystem ismadeupofmanysmallringlets.Theringletsaremadeupof icymatter.Itsspecificgravityislessthan that of water.
IthasmanysatellitesamongwhichTitanisofspecialinterest.Itistheonlynatural satellite which has its own atmosphere in the solar system.Saturnhasspecificgravityof0.13.Itisthelowestwhencomparedtootherplanets.Itsperiodofrotationandrevolutionare10hrs15minutes and29.46yearsrespectively.

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Uranus

Uranusistheseventhplanet from Sun anditisthethirdlargestplanet.Itisapeculiarplanetinthesensethatitsaxisofrotationhasatiltofabout .ExceptVenusalltheplanetsrotatefromwesttoeastwithsometilt.Uranushas a specific gravity of 0.29. Its period ofrotationandrevolutionare13hoursand84.02yearsrespectively.Thisplanetappearstorotateonverticalaxis.

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Neptune

Neptune is the eighth planet from the Sun.The planet Neptune can be seen only with the help of a telescope. Earlier its existence was predicted by mathematical calculations.Its specific gravity is 0.3. Its period of rotation and revolution are 18 hrs 30 minutes and 164.81 years respectively.

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Pluto

Earlier Pluto was considered as a planet of the solar system. But in 2006 the International Astronomical Union(IAU) adopted a new definition of a planet and according to this Pluto does not qualify as a planet of the solar system. However it continues to be a member, of the solar system. It is also called dwarf planet.