The Solar System ; Part of The Galaxy || The Solar System and the Earth


The solar system includes the sun and eight planets which revolve about it , held by gravity. The sun is a star and it is just one star among the hundred billion stars of the Milky Way galaxy. However, the sun’s Uniqueness lies in the fact that it possesses a planetary system. But it is possible to accept planetary systems for other stars also. 

Solar system is located at a distance of 8500 parsecs away from the centre of the galaxy. It revolves about the centre in a period of 200 Ma at a speed of 240 kbps.


The sun is the nearest star and forms the centre of the solar system. It may be considered as the head of the solar family. All the other members of the family revolve about the sun. It is a self luminous body radiating and radiating energy. It is the chief source of energy for all activities in the solar system. The sun is a star generating its own energy and producing light. It is the heaviest body in the solar system. It is 1000 times as heavy as the rest of the members of the system. This huge mass results in the rise of temperature to the order of millions of degrees Celsius. At this high temperature and pressure a nuclear fusion of hydrogen takes place resulting in the production of helium. This nuclear reaction is the reason why the sun is so shiny, so hot and so energetic. 

Another physical property that is resulted because of its massiveness is the gravity which controls the entire system. 

The visible luminous surface of the sun’s photosphere. The chromosphere is the high temperature gaseous layer surrounding the chromosphere. 


Planets are satellite bodies of a star revolving around that star under the pull of gravity. There are eight planets in the solar system. Planets of the solar system may be classified into two groups as inner planets and outer planets. This grouping has been done on the basis of the variation observed in the physical and chemical properties among the planets. 

Inner planets

The group of inner planets comprises the planets mercury, venus, Earth and Mars. Owing to their resemblance to earth they are also known as terrestrial planets. The terrestrial planets are small in size, less massive, more dense and have low angular momentum. They are mostly composed of rocks and metals. 

Outer planets –

This group consists of Jupiter, Saturn, Uranus and Neptune. They are large in size thus sometimes they are called Giant planets or jovian planets. These massive planets have low density but high angular momentum. They are mostly gaseous and possess a vast atmosphere. 


 Mercury is the innermost and closest planet to the sun. Mercury is 2.5 times smaller than the earth and mass is 1/20th of that of the earth. Density is smaller than Earth’s. It is similar to the moon having craters, mountains and lava plains. Atmosphere is meagre. It’s surface temperature is due to little atmosphere and proximity to the sun. The temperature is high enough to melt lead and tin. It has a dense core making 80 percent of the interior. The characteristic feature of the mercurian surface are shallow cliffs of several hundreds of kilometres in length. It has a low magnetic field. 


 Venus is between Mercury and earth. Venus is identical in many aspects with the earth . Both have similar size, mass and density. Venus is nearest to earth with a minimum distance of 41 mkm from the earth. It is geologically active. Recently volcanic lava flows have been recognised  on its surface. The dense atmosphere gives brilliant illumination to the planet and is called a morning and evening star in the Western and Eastern sky. The dense atmosphere produces a green house effect and the surface temperature is shot up to 480degrre centigrade. Pressure is calculated as 91 atmospheres of the earth . It’s atmosphere is chiefly composed of co2. 


The planet earth has been extensively studied . The third planet from the sun, the earth is unique among the system’s various planets. Because it sustains the biosphere. The Earth is the only planet to have liquid water and be geologically active. 78% Nitrogen and 21%oxygen make the atmosphere. The young ocean floors and old continent are the surface features. Hydrological cycle and internal thermal cycle are important factors for the geological activities. Evidence shows that the earth’s interior is segregated according to physical and chemical properties of the material into 3 distinct spherical layers as core, mantle and crust. Earth has one satellite, the Moon. 


Mars is the fourth planet revolving around the sun is an elliptical path beyond the earth. Mars is half the size of the earth with a mass of 1/10 of that of the earth. 

 Mars atmosphere is thin and consists of water ice, carbon dioxide, nitrogen, krypton and xenon. The atmospheric pressure is low. The surface temperature varies below  the freezing point. It’s soil’s red color gives a reddish shine to the planet. The surface feature such as valleys, volcanoes and craters are of gigantic proportions. Mars has two satellites namely phobos and Deimos. In size they are smaller and are comparable to asteroids. 


Jupiter is the largest and the most massive planet of the solar system and is the fifth one from the sun. It is ten times as big as the earth having a mass equal to 318 times that of the earth. The density is 1.34 it’s, it’s albedo is 0.54 . Several dark belts and light zones of atmosphere clouds are found parallel to the equator of the planet. The predominant weather modifiers are water, ammonium hydrosulphide and ammonia. The surface may contain liquid hydrogen and helium. The core may have a temperature of 30000 K. This is enveloped by liquid hydrogen layers. 

An important feature of Jupiter is the great red spot with a width of 14,000 km and ranging in length from 30,000 km to 40 , 000 km. The great red spot is considered to be a gigantic hurricane like one. This spot revolves around the planet. Jupiter has a ring system whose thickness is 6000 km. The ring seems to be a permanent feature. The loss of material by diffusion is gained by in-falling comets, meteoroids, and volcanic material of inner satellites. 

Satellites:  fifteen known satellites of Jupiter grouped into 1.inner group, 2.smaller group and 3. Outer group. Size ranges from the size of mercury to earth’s moon. The inner larger group satellites are collectively called Galilean satellites . They are lo, Europa, Ganymede and Gallisto. 


Saturn is the sixth planet with an elaborate ring system in the solar system. Saturn is the second largest planet having a lower density than water. It is 9 times the size of the earth with a mass of 95 times the earth’s mass. 

Saturn is a multilayered globe of gas with a core of iron and Rocky material to a radius of 13,800 km. It appears through a telescope as a pole -flattened sphere embedded in a ring system. 

Several dark belts and light zones of clouds of gases are found parallel to the equator of the planet. Wind speed exceeds 800kps . Temperature range between 82°k -143°k . Saturn has a special Characteristic that is the ring system and it is decided into F ring A- ring, B -ring and C -ring 


inner satellites of the planet are Janus, Mimas, Enceladus, Tethys, Dione and Rhea. These are spherical in shape and composed of water-ice. Outer satellites are Titan, Hyperion, Lapetus and phoebe. Apart from the satellites mentioned above there are very small satellites several hundred Kilometres in size. Titan is the largest. Nitrogen is the chief component of the atmosphere. Rivers and lakes of methane may be found on its surface. Chemically life forms may exist if temperature conditions allow. 


Uranus is the seventh planet from the sun. It is 31/2 times as big as the earth and possesses a mass of 14 1/2 times as that of the earth. 

The interesting fact about this planet is that it rotates about an axis almost Parallel to the ecliptic plane. It’s rotation is retrograde, like venus. The planet possesses a ring system with nine rings. Each pole of the planet will be illuminated by sunlight for a period of 42 years. 

Satellites-  Miranda, Ariel, Umbriel, Titania and Oberon are the satellites revolving the planet in a perpendicular planet to the planet’s ecliptic. 


Neptune was Theoretically predicted from the Perturbations of Uranus ‘ motion. This planet, invisible to naked eye, is the eighth one in the solar system. Size is four times the earth’s size and mass is 17 times that of the earth. 

A thick layer of atmosphere is indicated by its high albedo. It has not completed one complete revolution after it’s discovery since it’s sidereal period is equal to 165 years; it is almost similar to Uranus in size, mass and composition. 

Satellites –

Neptune has two satellites namely Triton and Nereid. Triton is the larger one and is retrograde in motion.

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