Solar System

Our solar system consists of a Star (sun), 8 Planets, 5 Dwarf Planets and countless fragments of left-overs called asteroids, meteors, comets and satellites of the planets (Called small solar system Bodies).


Various theories have been given by different persons to explain the origin of Solar System.

Gaseous Hypothesis Kant
Nebular Hypothesis o Laplace
Planetesimal Hypothesis Chamberlain and Moulton
Tidal Hypothesis James Jeans & Harold Jeffrey
Binary Star Hypothesis H. N. Russel
Fission Hypothesis Ross Gun
Cepheid Hypothesis A. C. Banerji
Nova Hypothesis Hoyle & Lyttleton
Electromagnetic hypothesis H. Alfven
Interstellar Dust Hypothesis Schmidt
Nebular Cloud Hypotheses Dr. Von Weizsacker
Protoplanet Hypothesis G. Kuiper


It is one of the stars in the milky way galaxy. It takes 224 million years to complete one circle revolution) around the galactic circle (called cosmic year) The sun is 109 times bigger than the earth and weighs 2 x 1027 tons.

Its glowing surface, which we see, is called photosphere. Above the photosphere is the chromosphere. Beyond chromosphere is the corona which is visible during eclipses.

The core of the sun has the temperature about 15 million degrees K.

Superimposed on suns white light are hundreds of dark lines called Fraunhoferines. Each line indicates some element present in the solar atmosphere.


Average distance From Earth 14,95,98,900 km
Diameter 13,91,980 km
Temperature at Core 1,50,00,000 °C
Temperature at Photosphere 5,760°C
Rotation Period 25 days (at equator), 33 days (at poles)
Chemical Composition Hydrogen-70%, Helium-28%, Others-2%
Age 4.6 billion years (approx.)
Expected Lite 10 billion years (approx.)
Time token by light to reach from Sun to Earth 8 min 16.6 sec.
Velocity of light (in vacuum) 3,00,000 km/sec.
Gravitational Pull 28 times than that of Earth

The Sun is constantly emitting streams of its substance (mainly hydrogen) as protons in all directions. Sometimes these emissions are massive. Such emissions are called Prominence.

Sometimes these emissions roll out of the atmosphere of the sun for thousands and thousands of miles, when they are seen as Solar Flares.

Persistent stream or protons and electrons is blowing out of the corona and sweeping over the whole Solar system. This stream is called Solar Wind.

The earth s magnetosphere acts as a shield against the ever-blowing solar wind and deflects it away from the earth. Nevertheless, particles of solar wind sometimes pierce the magnetic shield and enter the upper atmosphere, where, like the solar flares, they cause aurora displays. In the Arctic region, they are called Aurora Borealis and in the Antarctic region, they are known as Aurora Australis.

The surface of the sun changes continuously. Bright spots called Plages and dark spots called Sunspots Occur there. sunspots appear dark because they are cooler, i.e., they have a temperature of about 1500°c. Sunspots have a periodicity of 11 years.

The energy of sun comes from the fusion of hydrogen into helium. Sunlight takes 8 min, 16.6 sec to reach earth.

Ecliptic is an imaginary annual path of Sun across the sky.

Its age is 5 billion years and the total life is 10 billion years.



The 2006 redefinition of "planet" by the International Astronomical Union (IAU) states at, in the solar system, a planet is a celestial body that:

  1. is in orbit around the Sun.
  2. has sufficient mass so that it assumes a hydro-static equilibrium (nearly round) shape.
  3. has cleared the neighborhood around its orbit.

A non-satellite body fulfilling the first two of these criteria is classified as a Dwarf planet, whilst a non-satellite body fulfilling only the first criterion is termed a Small Solar System Body (SSSB).

According to the definition, there are currently eight planets and five dwarf planets known in the solar system. The 5 dwarf planets are Pluto, Ceres, Eris, Makemake and Haumea.

Planets are divided into two groups: large, low-density gas giants and smaller rocky terrestrials.

Under IAU definitions, there are 8 planets in the Solar System- Mercury, Venus, Earth, Mars (called Terrestrial Planets), Jupiter, Saturn, Uranus, Neptune (called Jovian Planets).

Planets according to size: Jupiter, Saturn, Uranus, Neptune, Earth, Venus, Mars and Mercury.


  • Rotation: 58.65 days.
  • Revolution: 88 days (Fastest revolution in Solar System).
  • Maximum diurnal range of temperature. Its days are scorching hot and nights are frigid.
  • it has no atmosphere and no satellite.


  • Also called Earth's Twin, because it is slightly smaller than earth (500 km less in diameter).
  • Popularly known as Evening star and Morning star. It is seen in the east in the Popularly known morning and in the west in the evening. It is not possible to see it all over the night.
  • Brightest object after sun and moon (because of 70% albedo, the reflecting power).
  • Closest planet to earth.
  • It is the hottest planet in Solar System. It is because of the Green house effect as its atmosphere contains 90-95% carbon dioxide. The night and day temperatures almost the same.
  • Rotates backward (clockwise) unlike others.
  • It has no satellite.
  • Slowest rotation in Solar System (257 days). Almost equal rotation and revolution (224.7 days).


  • Also called Blue Planet. It is the densest of all planets.
  • Circumference: 40,232 km., Area: 510 million sq. km., Average distance from sun: 149 million-km.
  • Perihelion: Nearest position of earth to sun. The earth reaches its perihelion on January 3 every year at a distance of about 147 million-km.
  • Aphelion: Farthest position of earth from sun. The earth reaches its aphelion on July 4, when the earth is at a distance of 152 million km.
  • The shape of the earth is oblate spheroid or oblate ellipsoid (i.e. almost spherical, flattened a little at the poles with a slight bulge at the center).


  • Also called Red Planet.
  • Revolution: 687 days.
  • Rotation: 24.6 hrs (almost equal to Earth).
  • It has a thin atmosphere comprising of nitrogen and argon.
  • It is marked with dormant volcanoes and deep chasms where once water flowed.
  • Recent explorations have thrown light on the possibilities of existence of life here.
  • The highest mountain here is named 'Nix Olympia', which is three times higher than Mount Everest.
  • It has 2 satellites- Phobos and Deimos.


  • Largest of all planets (71% of the total mass of all planets). Called Lord of the Heavens.
  • Jupiter appears to have stopped halfway to becoming a star. It was too massive to solidify as a planet but not massive enough to develop 'nuclear fusion' and become a star.
  • It gives off more energy than it receives from the sun, because of the heat inside.
  • Its atmosphere contains hydrogen, helium, methane and ammonia.
  • A great red spot is detected on it. It represents a huge storm- a super hurricane, existing for hundreds of years, without abating. This storm is probably powered by Jupiter's internal heat.
  • It has the fastest rotation time(9.8 hr) in the Solar System.
  • Revolution: 12 years.
  • It has 63 satellites (Prominent are Europa, Ganymede & Callisto). Ganymede is the largest satellite of Solar System.


  1. Second in size after Jupiter.
  2. Revolution: 29 yrs. Rotation: 10.3 hrs.
  3. Least density of all (30 times less dense than earth).
  4. Unique feature is its system of rings (3 well defined). These are separate particles that move independently. in circular orbits.
  5. 62 satellites (Prominent is Titan).
  6. The space probe, Cassini, is on Saturn these days.


  • Identified as a planet in 1781 by William Hershel.
  • Seems to rotate from north to south as it is inclined at an angle of 98° to its orbit.
  • Revolution: 84 yrs. Rotation: 10.8 hrs.
  • Surrounded by a system of 9 faint rings.
  • Has 27 satellites (prominent are Miranda, Ariel, etc)


  • Appears as 'Greenish Star.
  • Revolution: 165 yrs. Rotation: 15.7 days.
  • Has 5 faint rings.
  • Discovered by JG Galle of Berlin in 1846.
  • 13 satellites (prominent are Triton and Nereid).


  • Pluto is the second largest known Dwarf Planet in the Solar System.
  • Since its discovery by Clyde Tombaugh in 1930, Pluto was considered the ninth planet from the Sun. In August, 2006, the International Astronomical Union (1AU) redefined the term planet, and classified Pluto, Ceres, Eris, Makemake and Haumea as Dwarf Planets.
  • Now, Pluto has been given the number 134340.


1. Biggest Planet Jupiter
2. Smallest Planet Mercury
3. Nearest Planet to Sun Mercury
4. Farthest Planet from Sun Neptune
5. Nearest Planet to Earth Venus
6. Brightest Planet Venus
7. Brightest star after Sun Sirius
8. Planet with maximum satellites Jupiter
9. Coldest Planet Neptune
10. Hottest Planet Venus
11. Heaviest Planet Jupiter
12. Red Planet Mars
13. Biggest Satellite Ganymede
14. Smallest Satellite Deimos
15. Blue Planet Earth
16. Morning/Evening Star Venus
17. Earth's twin Venus
18. Green Planet Neptune
19. Planet with a big red spot Jupiter
20. Lord of the Heavens Jupiter
21. Greatest Diurnal Temperature Mercury


Circumference: 11,000 km. Diameter: 3475 km. Gravitational pull: 1/6th of Earth.

Its orbit around earth is elliptical. The maximum distance (Apogee) of the moon from the earth is 406,000 km and the minimum distance (Perigee) is 364,000 km. the average distance is 3,82,200 km.

  • All other satellites (except Charon) have sizes below 1/8th the size of mother planets.
  • But moon is about 1/4th the size of earth.
  • Takes 27 days, 7 hrs, 43 min and 11.47 sec to complete one revolution around earth.

Rotates on its axis in exactly the same time as it takes to complete one revolution. That is why we see only one side of the moon (only 59% of its surface).

To our unaided vision, moon seems to be made-up of bright and dark patches. The bright parts are the mountains and highlands, while the darker patches are low-lying planes.

The highest mountains on moon are Liebnitz Mountains, which are 10,660 m high. They are situated at moon's South Pole.

  • Moon has no atmosphere, no twilight and no sound.
  • Moonlight takes 1.3 sec to reach earth.

It has a low albedo (amount of sunlight reflected). It reflects only 7% and the rest is absorbed (Earth: 30%, Venus: 70%)

Neil Armstrong and Buzz Aldrin reached moon on July 20, 1969 on Apollo XI and set the foot on July 21, 1969 (landing spot is called Sea of tranquility).


1. Distance from Earth 3,82,200 km
2. Diameter 3,475 km
3. Mass with respect to Earth 1:8.1
4. Ratio of Gravitational Pull Moon and Earth 1:6
5. Part of Moon not visible from Earth 41%
6. Maximum distance from Earth (Apogee 4,06,000 km
7. Minimum distance from Earth (Perique) 3,64,000 km
8. Revolution period around Earth 27 days, 7 hrs, 43 min and 11.47 sec
9. Rotation period 27 days, 7 hrs, 43 min and 1147 sec
10. Atmosphere Absent
11. Highest mountain 35,000 f (Leibnitz Mts.)
12. Time taken by moonlight to reach Earth 1.3 sec
13. Rotation speed 3,680 kmph
14. Speed of revolution around Earth 3,680 kmph


Asteroids are a series of very small planets or fragments of planets lying between the orbits of Mars and Jupiter. Also called Planeloads or small planets'.

  • They revolve around the sun in the same way as the planets.
  • They are too small to retain any atmosphere of their own.

Asteroids are presumed to be the remnants of matter that did not clump during the formation of the solar system. Even if the materials did collide, the gravity from Jupiter pulled them apart from each other.

Composed of rock, dust and metal, the early asteroids were formed when the heavy metal within them sunk to the center of the rock, forming a metal core. Over time, the lighter rocks formed layers around the core. The rock would then cool steadily, eventually becoming a solid.

Currently, the largest object in the asteroid belt, Ceres, at about 950 km diameter, has been placed under Dwarf Planet category.


It has a head and a tail. Its tail originates only when it gets closer to the sun. The tail can be 20-30 million km long. It always point away from the sun because of the force exerted by solar wind and radiation on the cometory material.

Comets may originate in a huge cloud called the oort cloud that is thought to surround the Solar System.

  1. Hailey's comet: Reappears after 76 years. Last seen in 1986.
  2. Comet Smith-Tuttle: Can collide with earth on Aug 17, 2116. Will create an impact
    of about 1.6 million times that of Hiroshima bomb.
  3. Comet Shoemaker Levy-9: Collided with Jupiter between July 16 and 21, 1994.

METEORS (Shooting Stars)

The meteors are probably the remains of comets which are scattered in the inter-planetary space of the Solar System. On contact with the earth's atmosphere, they burn due to friction.

Sometimes an unusually large number of meteors can be seen in rapid succession. Such a display is called a meteor shower and occurs when the earth passes through a swarm of meteoroids.

Largest known is of 70 tons, which landed in Namibia in pre-historic times.


Planet Distance from Sun (in million km) Diameter (in km) No. of Satellites Rotation period Revolution Period
Mercury 5.79 4878 0 58.65 days 88 days
Venus 10.82 12102 0 257 days 225 days
Earth 14.96 12755 1 23 hrs, 56 min, 40.91 sec 365 days, 5 hrs, 48 min, 45.51seec
Mars 22.79 6787 2 Almost 24 hrs 687 days
Jupiter 77.83 142800 63 9.8 hrs 12 years
Saturn 142.70 120500 62 10.3 hrs 29 years
Uranus 287.96 51400 27 10.8 days 84 years
Neptune 497.06 48600 13 15.7 days 165 years