Solar Family

The giant family of the sun including planets, asteroids, comets etc is called the solar system. Solar system is composed of the sun and the heavenly bodies in the gravitational field of the sun. The diameter of the solar system is 1.87 light years.

Sun:

The sun is a medium-sized light yellow colored star whose diameter is about 1392000 km and is situated at about 2.5 × 10⁴ light years away from the galactic center of the Milky Way. The distance between the sun and the earth is about 1.5 × 10⁸ km. About 75% of the total mass of the sun is made up of hydrogen and slightly lesser than 25% of the mass is made up of helium and the rest is composed of carbon, oxygen, and other elements. The temperature of the surface of the sun is 6 × 10^3 oC and that of the core is 1.5 × 10^{7 o}C. The mass of the sun is about 2 × 10³⁰ kg. It takes 2.5 × 10⁸ years to complete one revolution around the galactic center ad that period is called one cosmic year.

The sun is made up of three layers: Photosphere, Chromosphere, and Corona. Photosphere is the central hottest and thinnest layer. The chromosphere is thicker than photosphere and is visible only during the total solar eclipse. Corona is the thickest layer which is spread about millions of kilometers around the chromosphere. The sun produces most of the energy by nuclear fusion on its core.  

Importance of sun in solar system:

1. It is the center of solar system.
2. All the planets revolve around the sun in their own orbit.
3. It provides light to all the planet to shine as they have no light of their own.
4. It provides heat and light energy for the lives of the planets if the life exists there.

Planets are the heavenly bodies that revolve around the sun in their own separate elliptical orbits. In the solar system, there are eight planets and out of them, the first four planets which are present inside the asteroid belt are called inner planets. They are Mercury, Venus, Earth, and Mars. But the remaining four planets are out of the asteroid belt and are called an outer planet. They are Jupiter, Saturn, Uranus, and Neptune.

A brief description on each planet is as follows:

Some important facts about planet:

Satellites

Satellites are the heavenly bodies that revolve around the plants. They may be natural or artificial. 

1. Natural satellite:
   They are the member of the solar system which revolves around the planets in their elliptical orbits. There are about 175 natural satellites. Every planet does not have satellites. Mercury and Venus do not have satellite. Despite being a non- luminous body, the satellite appears bright by reflecting light from the sun. The number of satellite varies from one to another planet:
   
   

   S.No.	Planet	No. of Satellite
   1.	Mercury	0
   2.	Venus	0
   3.	Earth	1 [Moon]
   4.	Mars	2 [Phobos and Deimos]
   5.	Jupiter	67 [Europa, Io, etc.]
   6.	Saturn	62 [Titan, etc.]
   7.	Uranus	27 [Miranda, Arial, etc.]
   8.	Neptune	14 [Triton, Nereid, etc.]

   _{Source: Encarta - 2009}      
   
   Moon,  the natural satellite of Earth, is the only satellite of earth having about 30 plains, 30000 craters, and several mountains. The equatorial diameter of the moon is 3476 km and the mean distance between the earth and the moon is about 385000 km with a surface area of about 37940000 km². Its gravity is one-sixth of that of the earth. Neil Armstrong, an American astronaut, was the first person who stepped on the moon on 20th July 1969 AD. He was accompanied by Edwin Aldrin and Michael Collins. They landed safely on earth after doing some simple experiments, taking photographs and samples of rock.
   
   
2. Artificial satellite:
   A satellite which is made on earth to revolve around the earth or any other heavenly body is said to be an artificial satellite. It has an elliptical orbit which is characterized by three parameters apogee, perigee, and inclination. There are various purposes for which a satellite is launched. Some of them are:
   
   - Weather Satellite: To study overall weather patterns of the earth.
   - Communication Satellite: To improve the quality and speed of mass communication.
   - Navigation Satellite: To know the exact position of navigators in air or ocean in any weather.
   - Scientific Satellite: To gather information about the universe.
   - Military Satellite: To observe troop movements, spy military base by military intelligence.

Asteroid:

The piece of rocks revolving around the sun between the orbits of Mars and Jupiter are known as asteroids. It varies in diameter and there are about 200 asteroids are present in the solar system. They are also known as minor planets or baby planets or planetoids. They are composed up of various rocky and metallic substances. Juno, Vesta, Hermas, Eros, Pallas, etc. are some of the asteroids present in the solar system. The Ceres is kept in the group of Dwarf Planet and Pallas is the biggest asteroid with a diameter of 532 km. 

Comet:

A frozen chunk of gas, dust, and ice which begins to resemble a foggy star with a long shiny tail when it approaches the sun is known as comet. The comet can be divided into three parts: nucleus, coma, and tail. The nucleus is made from frozen gases, ice, and dust. When it approaches the sun, the outer layer of nucleus starts to evaporate, which is known as coma. The nucleus and coma combine is said to be head of a comet. When it approaches nearer to the sun, pressure from the solar wind elongates the coma, the elongated part of comet said to be tail of the comet. It is always pointed away from the sun. As the orbit of the comet around the sun is highly elliptical, sometimes it has to pass very close to the sun and sometimes very far from the sun. They are non- luminous bodies, which appear bright by reflecting the light of the sun, so they are termed as tailed stars.

Halley's Comet is a very common comet discovered by an English astronomer, Edmond Halley in 1682 AD. Name and revolution period of some other comets are given below:

 

Meteors and Meteorites:

Small pieces of rocks or metals which enter the earth's atmosphere from outer space with very high speed are called Meteors. They are also called the falling star or shooting star. Usually, meteors are burn from the height of 7 km to 120 km and during this, the time velocity of meteors is about 70 km/s. We can see the meteor showers in the sky of the north and south poles.

If meteors are too big, then it will not burn completely and reach on earth, which is called the meteorite. They form a crater on the surface of the earth. It can be mainly classified into three types: Stony, Irony, and Stony- Irony. Stony meteoroids have more silica whereas irony meteoroids have more iron and magnesium. Stony- irony meteoroids have silica and iron both in a balanced amount. 

The largest meteorite found in Hoba West near Groofontein, in South West Africa, weighs about 60000 kg and is still at the original spot where it struck the earth. It is named Hoba. About 35000 kg, moderately weighing meteorite, is in the American Museum of Natural History in New York City and was discovered in 1894 AD by Admiral Peary in Greenland. A meteorite that formed a crater of 1265 m in diameter and 174 m in depth fell at Arizona of America, about 50000 years ago.