• The sun accounts for more than 99 per cent of the mass of the solar system and due to this the sun exerts immense gravitational pull to keep the planets rotating around it indefinite elliptical orbit
  • The sun is the major source of energy in the solar system
  • The energy is provided by the nuclear fusion reaction, that converts hydrogen into helium in the core of the sun
  • The glowing surface of the sun that we see is called a photosphere
  • Above the photosphere is the red coloured chromospheres and beyond it is the magnificent corona, which is visible during the eclipse
  • Hydrogen and helium are the main gases present in the sun
  • It has a surface temperature of about 6000. C
  • It takes 224 million years to complete one circle around the galactic circle called a cosmic year
  • The sun is 1300000 times bigger than the earth in terms of volume
  • Superimposed on the sun’s white light are hundred of dark lines called Fraunhofer lines. Each line indicates some elements present in the solar system
  • The rotational speed of the sun is 25.38 days
  • Time taken by the sun to reach the earth is 8minutes and 16.6 seconds

Concepts associated with the sun

  • Solar winds-the sun is continuously emitting streams of photons in all direction either as spiral streams called solar wind or bouts of incandescent material called solar flares
  • Solar flares being hot ionized gases pose danger to satellite communication
  • Aurora – the constituent particles of the solar wind are trapped by the earth’s magnetic field and enter the earth’s upper atmosphere as aurora
  • It is described as aurora borealis in the northern hemisphere and aurora australis in the southern hemisphere
  • Plages and sunspots– the surface of the sun is continuously changing; bright spots are called Plages and dark spots are called sunspots
  • The sunspots are cold and dark regions on the sun’s surface with a periodicity of 11 years
  • These spots greatly influence the global climate

The planets

  • Planets are opaque bodies that continuously revolve around and are lighted by the sun
  • There are eight planets in the solar system
  • The sequence of planets according to their size is Jupiter, Saturn, Uranus, Neptune, Earth, Venus, Mars and mercury
  • The sequence of planets according to their distance from the sun is Mercury, venus, earth, Mars, Jupiter, Saturn, Uranus and Neptune

Classification of planets

  • Inner planets include Earth, Venus, and mars
  • Outer planets include Jupiter, Saturn, Uranus, and Neptune

Inner planets are called terrestrial or rock planets. They are nearer to the sun. they have very few natural satellites(moons). They have a core of molten metals. They move faster and have a shorter period of revolution

Outer planet is called Jovian or gaseous planets. They are far away from the sun. they have a large number of natural satellites(moons). They have a ring system around the sun. they move rather slowly and have a longer period of revolution

Specifics of the planets

  • The biggest planet Jupiter
  • The biggest satellite Ganymede
  • The blue planet earth
  • The green planet Uranus
  • The brightest star outside the solar system Sirius (the dog star)
  • The closest star of the solar system Proxima Centauri
  • The coldest planet Neptune
  • The evening star Venus
  • The farthest planet from the sun Neptune
  • The planet with the maximum number of satellites Jupiter (62)
  • The planet with the fastest revolution in the solar system mercury
  • The hottest planet Venus
  • The densest planet earth
  • The fastest rotation in the solar system Jupiter
  • The morning star Venus
  • The nearest planet to earth Venus
  • The nearest planet to the sun mercury
  • The slowest revolution planet in the solar system Neptune
  • The slowest motion in the solar system Venus
  • The smallest planet mercury
  • The smallest satellite Phobos
  • Earth’s twin Venus
  • The only satellite with an atmosphere like earth titan


  • The smallest and the innermost planet
  • It has no atmosphere
  • It has a crated surface, much like the moon
  • It has the maximum diurnal range of temperature
  • It has no moons


  • Also called the veiled planet and evening and morning star as it is in the east in the morning and in the west in the evening
  • It is the brightest object in the solar system because of almost 70% albedo
  • It contains 90 to 95% of CO2
  • The night and day temperature is almost the same
  • It has the slowest rotational speed.
  • It has a rotation of 257 days and a revolution of 224.7 days
  • Rotates from east to west, unlike the other planets.
  • It is the hottest planet
  • It has no moons


  • The earth is neither too hot nor too cold
  • It is called the blue planet due to the presence of water
  • It has a rotation of 24 hrs and a revolution of 365 days and 6 hours
  • Moon is the only natural satellite


  • Called as the red planet
  • It has a thin atmosphere compromising of nitrogen and argon
  • It has a rotation of 24.6 hours and a revolution of 687 days
  • It has two moons Phobos and Deimos


  • It is the largest planet in the solar system with a mass 2.5 times greater than the combined mass of all the remaining planets, satellites and asteroids together
  • It contains hydrogen, helium, methane and ammonia
  • A great red spot is detected on it
  • It has the fastest rotational velocity of 9.8 hrs
  • It is 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
  • It has 67 satellites, some of the prominent satellites are Europa, Callisto, and Ganymede
  • These are called galileon moons


  • It is the 2nd largest planet and is surrounded by a set of eight rings
  • The rings are made up of primordial dust and ice particle
  • The rotations are 10.3 hours and a revolution of 29 ½ years
  • It has the least density of all the satellites
  • 30 times less dense than the earth
  • It has 62 satellites, the largest being titan


  • It is unique as its axis of rotation is inclined at 98 to its orbital plane
  • Unlike the others which spin on their axis. Uranus actually rolls, apparently from north to south
  • Surrounded by a system of 9 faint rings
  • It has 27 satellites. The prominent is Miranda, ariel etc


  • It is a penultimate planet that has a dynamic atmosphere, which contains the earth-sized blemish called the great dark spot that is reminiscent of Jupiter’s red spot
  • The rotation is about 15.7 days and revolution of 165 years
  • It has 5 faint rings
  • It appears as the greenish star
  • It has 14 satellites. the prominent are triton and nereid

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