Note on Solar Family

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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.


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 × 103 oC and that of the core is 1.5 × 107 oC. 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:

S.No. Name of Planet Mean distance from the Sun Diameter (km) Temperature (oC) Period of Rotation Period of Revolation Number of Satellite Mass (Earth = 1) Atmosphere
1. Mercury 5.8 × 107 4880 427oC at day and -170oC at night 59 days 88 days 0 0.056 Nil
2. Venus 1.08 × 108 12104 480oC 243 days 225 days 0 0.815 90-95%, CO2, clouds of H2SO4
3. Earth 1.5 × 108 12756 22oC About 24 hrs. About 365 days 1 [Moon] 1 N2 (78%), O2 (21%), CO2, H2O etc.
4. Mars 2.26 × 108 6720 20oC at day and -143oC at night 24 hrs. and 37 mins 687 days 2 [Phobos, Diemos] 0.1 Thin CO2, little water, little O2
5. Jupiter 7.68 × 108 140800 -150oC about 10 hrs. [9hr. 55 mins] About 12 yrs. 67 [Europa, Io, Callisto] 318 H2, He
6. Saturn 1.5 × 109 120585 -180oC 10 hr. 14 min 29.5 yrs. 62 [Titan] 95 H2, He
7. Uranus 2.87 × 109 51200 -216oC 17 hr. 8 mins 84 yrs. 27 [Miranda, Ariel, Umbrial] 15 H2, He, CH4
8. Neptune 4.48 × 109 48000 -220oC 16 hrs. 164 yrs. 14 [Triton, Neried] 17 H2, He, CH4
Some important facts about planet:
S.No. Characteristics Name of Planet
1. Nearest planet to sun Mercury
2. Farthest planet to the sun Neptune
3. Fastest rotating planet Mercury
4. Morning and evening star Venus
5. Hottest planet Venus
6. Green planet or living planet Earth
7. Red planet Mars
8. Largest planet Jupiter
9. Planet having ring Saturn
10. Planet that can float in water Saturn

The International Convention of International Union of Astronomers (IUA) held on 2006 in Prague of Czech Republic has removed Pluto from the list of planets and introduced a new term, Dwarf planet for it. A new definition of the planet has been given by the convention. According to it:

 - A planet should have its own orbit around the sun.

 - It must be in round shape.

 - It must have a fixed neighborhood with other planets.



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.


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. 


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:

Comets First Seen (AD) Revolution
Temple- tutle 1366 33 years
Enke 1786 3.33 years
Donati 1858 2000 years
Schwasman- Washman 1972 15 years
Shoemaker- Levi 1993 Collided in 1994 AD in Jupiter
Hyakutake Comet 1996 20000 years

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.



  • The giant family of sun including planets, asteroids , comets etc is called solar system.
  • In solar system there are eight planets and out of them first four planet which are present inside asteroid belt are called inner planets.
  • The piece of rocks revolving round the sun between variable size are asteroids.
  • A comet is a frozen chunk of gas,dust and ice which when approaches the sun it begins to resemble a foggy star with long shiny tail.

Very Short Questions

A group of heavenly bodies where sun is the center and all the other heavenly bodies are under the influence of its gravitational force is called the solar system. The solar system contains of the sun the nine planets, their satellites, a large number of asteroids, comets and meteors.

The sun mainly contains of hydrogen gas. The hydrogen atom continuously combines to form helium atoms. Four hydrogen atoms combine to form a helium atom by the process of nuclear fusion. During this nuclear fusion a huge amount of energy is released. ­­1H1+1H11H2­ ­­1H2+1H11H3­ ­­1H3+1H11H4­+ energy

Fragments of heavenly bodies that have irregular shape and revolve around the sun are called asteroids. These asteroids that are also known as minor planets revolve around the sun with their revolving orbit present between the revolving orbits of Mars and Jupiter.

Comet that appears every time after a fixed period of time as it takes a definite time to revolve around the sun is called periodic comet. Halley's Comet is a periodic comet that appears after every 76 years. It last appeared in 1986 and will again appear in 2062 AD. Hyakutake is another periodic comet.

One example of a comet is the Hyakutake Comet. The comet revolves around the sun like planets but the orbit is much larger than those of planet. Because of this reason each comet is seen at a gap of long period.

Comet is a small object with a head and a tail. Head is the main body made up of hard particles of methane, water and ammonia embedded in ice. The tail consists of dust or gas. As the comet approaches the sun, the crystal vaporizes and gas glows in the form of a long tail. When the comet moves away from the sun, the tail shortens due to less heat. This is why the tail of the comet increases or decreases when it goes round the sun.

Meteors are the pieces of heavenly bodies that burn to ashes due to friction on entering the earth's atmosphere. When meteor burns, a part of it reaches the earth's surface before burning completely to ashes. The piece that reaches the earth's surface is called meteorite.

The 5 importance of the sun are as follows:

  1. The sun emits continuous heat and light due to thermo-nuclear reactions making life possible on the earth.
  2. It is the cause for brightness seen in all the planets and satellites. The planets and satellites appear bright as they reflect the sun's light.
  3. The sun controls the outer layer temperature and becomes the central cause for different geographical processes on the earth.
  4. It is the major source of energy. Sun light can be converted into electrical energy by solar cells.
  5. All planets and natural satellites remain and revolve in the fixed orbits because of the sun.

When meteor falls, it comes in contact with the earth's atmosphere. The friction that results causes the meteor to burn completely to ashes leaving nothing to reach the earth's surface. Comet is a heavenly body that shines brightly when it comes near the sun. Comet is seen with a head and a bright tail because of sun's light. As it does not have its own light, it's not a star.

Three reasons of launching artificial satellite into the space are as follows:

  1. It is used for communication like radio, TV, telephone, e-mail, etc. For this purpose geo-stationary satellite is used.
  2. Satellite is used for forecasting the weather of a specific place or a country. This weather forecast is important for domestic and international flights of a country.
  3. Satellite can be used to study about other planets and natural satellite for this purpose, the artificial satellite sends photographs to the earth's control center.

  • The time interval between two successive occurrences of a specific type of alignment of a planet (or the moon) with the sun and the earth is referred to as ______.

    an opposition

    a synodic period.

    a sidereal period

    a conjunction

  • The giant family of sun including planets, asteroids , comets etc is called ______.

    solar system




  • The biggest asteroid is ______.





  • The largest circular storm in our solar system is on the surface of ______.





  • One Jupiter day is equal to ______.

    3 hrs 20 min

    52 hrs 10 min

    9 hrs 50 min

    30 hrs 40 min

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Forum Time Replies Report
prabin shrestha

why venus is taken as the twin planet of earth?

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Smallest planet

Smallest planet,brightest planet

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Evedience of black hole

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Dikshyant Adhikari

The comet is not a star ,why ?

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