Solar System

  • The branch of science that deals with the study of universe is called Astronomy.
  • The Solar System is the gravitationally bound system comprising the Sun and the objects that orbit it, either directly or indirectly.
  • A group of stars which form a recognizable pattern or shape is called a Constellation.
  • The brightest star, Sirius is located in the Constellation of Orion.
  • Hydra is the largest of the 88 modern Constellations.
  • The 8 planets in the order of increasing distance from the Sun are : Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.
  • Inner planets : The four planets Mercury, Venus, Earth and Mars are called the Inner planets or terrestrial planets.
  • Outer planets : The four planets Jupiter, Saturn, Uranus and Neptune  are the outer planets or Jovian planets or Gas giant.
  • Asteroids: They are tiny bodies that move around the Sun., found between the orbits of Mars & Jupiter.
  • Meteoroids: These are small rock pieces that move around the Sun.
  • Pluto was demoted to dwarf planet at 26th general assembly of International Astronomical Union held at Czech republic in 2006.


  • Smallest Planet and Closest to the Sun
  • Fastest planet in our Solar system.
  • Has no Satellites.
  • Revolves around the Sun in 87.969 days.
  • Period of rotation is 58 days.
  • Mercury is the only planet to have shrunk after it was formed.
  • The first spacecraft to visit Mercury was NASA's Mariner 10


  • Earth's nearest planetory neighbour.
  • Brightest planet in the solar system.
  • Known as the 'Evening Star' and  the 'Morning Star'.
  • Has no Satellites.
  • Revolves around the Sun in 224.7 days.
  • The first spacecraft to visit Venus was Mariner 2 in 1962
  • The atmosphere of Venus is heavier than that of any other planet.
  • Earth's 'Sister Planet' or Earth's 'twin'.
  • The clouds of Venus contains sulfuric acid. This causes acid rains in the planet.


  • Fifth largest planet of the solar system.
  • The average temperature of the Earth surface is 16°C.
  • Densest planet in the solar system. Known as the Blue Planet.
  • Earth takes 23 hours, 56 minutes, and 4.09 seconds to spin around once. This length of time is called Sidereal day.
  • Earth takes 365.25 days to complete one revolution around the Sun.
  • The Earth spins about its own imaginary axis from west to east.
  • On 21 June, the Earth is farthest from the sun in southern hemisphere.


  • Mars is the only planet whose surface can been seen in detail from the Earth.
  • Known as the "Red Planet", as the iron oxide prevalent on its surface gives it a reddish color.
  • It has two satellites: Phobos and Deimos.
  • Mars has approximately half the radius of Earth.
  • In 1997, a probe called Mars Pathfinder landed on Mars.


  • Largest planet in the solar system. It is 11 times bigger than the Earth.
  • Jupiter has 66 known satellites. The four largest moons, Ganymede, Callisto, Io and Europa were discovered by Galileo in 1610 and are called Galilean satellites.
  • Ganymede is the largest satellite in the Solar System. 
  • Jupiter takes 4331 days (12 years) to orbit the Sun.
  • Comet Shoemaker- Levy 9 was a commet that broke apart and collided with Jupiter in July 1994, providing the first direct observation of an extraterrestrial collision of solar system objects.  


  • Second Largest planet in the solar system.
  • It orbits the Sun in 29.46 years.
  • Known as "Ring Planet". Saturn's rings were discovered by Galilio.
  • Saturn has 62 recognised satellites. The Titan is the second largest satellite in the Solar System.
  • Saturn's atmosphere is 91% hydrogen by mass.


  • Third largest planet in the solar system.
  • Greenish in appearence due to the presence of methane gas.
  • Known as tilted planet. Its axis is tilted at an angle of 98°.
  • Discovered by Sir William Herschel on March 13, 1781.
  • Uranus has 27 known natural satellites. The largest of Uranus's satellites is Titania and the smallest is Cordelia.


  • Fourth largest planet in the solar system.
  • Neptune was first discovered in 1846 by Urbain Jean Joseph Leverrier.
  • Neptune is not visible to the unaided eye and is the only planet in the Solar System found by mathematical prediction rather than by empirical observation.
  • It has 14 known satellites. Triton is the largest Neptunian moon. 

Dwarf Planets

  • dwarf planet is a planetary-mass object that is neither a planet nor a natural satellite.
  • The term dwarf planet was adopted in 2006 as part of a three-way categorization of bodies orbiting the Sun.
  • The International Astronomical Union (IAU) currently recognizes five dwarf planets in the solar system: Ceres, Pluto, Haumea, Makemake and Eris.
  • Eris is the largest known dwarf planet in the solar system.
  • Pluto is the second largest known dwarf planet. It was discovered by Clyde Tombaugh in 1930.
  • Pluto's orbital period is 248.4 years.
  • Pluto has five known natural satellites: the largest being Charon, discovered in 1978.