Physics - The Solar System


  • The Sun and all the celestial bodies which revolve around it (the sun) are known as the solar system.

  • The solar system consists of a large number of bodies including planets, comets, asteroids, and meteors.

  • There are eight planets; they are arranged in their order of distance from the Sun as: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune (see the image given below).

  • The first four planets, Mercury, Venus, Earth and Mars, are known as ‘inner planets.’

  • Jupiter, Saturn, Uranus and Neptune are much farther off from the sun and known as ‘outer planet.’

Solar System

The Sun

  • The Sun is the nearest star from the earth.

  • The Sun is about 150,000,000 kilometers (150 million km) away from the Earth.

  • The Sun is the source of almost all energy available on the Earth.

  • After sun, Alpha Centauri, is the nearest star from the earth.

  • Light year is the distance travelled by light in one year.

  • The speed of light is about 300,000 km per second.

The Planets

  • There are eight planets that keep changing their positions with respect to the stars.

  • The planets have definite paths in which they revolve around the Sun.

  • The path of the planet is known as an orbit (see the image given above).

  • The time taken by a planet to complete one revolution is known as its period of revolution.

  • The time period of revolution increases with the distance of the planet increases from the sun.

  • All planet also rotates on its own axis, which is known as its rotation period.

  • A celestial body revolving around the planet is known as satellite or moon.

  • The planet mercury is smallest and nearest to the Sun.

  • Mercury has no satellite of its own.

  • Venus is the nearest planet to the earth.

  • Venus is the brightest planet.

  • Venus appears in the eastern sky before sunrise and appears in the western sky after sunset; therefore, it is also known as morning or an evening star.

  • Venus has no moon/satellite.

  • Venus rotates from east to west.

  • From space, earth appears blue-green due to reflection of light from water and landmass accordingly.

  • The Earth has one moon.

  • Mars appears somewhat reddish and, hence, known as the red planet.

  • Mars has two natural satellites.

  • Jupiter is the largest planet of the solar system.

  • Jupiter is about 318 times heavier than that of the Earth.

  • Saturn appears yellowish in color.

  • Saturn has rings around it.

  • Saturn is the least dense among all the planets (even water is denser than Saturn).

  • Like Venus, Uranus also rotates from east to west.

  • The most significant feature of Uranus is that it has highly tilted rotational axis.

  • There is a large gap between the orbits of Mars and Jupiter; it is filled with some objects known as ‘asteroids’ and this region is known as asteroid belt (see the image given below).

  • A Comet appears usually as a bright head with a long tail and the length of the tail grows in size as it approaches towards the sun (see image given below).

  • Halley’s comet appears after (nearly) every 76 years; last seen in 1986.

  • A meteor is typically a small object that occasionally enters the earth’s atmosphere.

  • Meteors are commonly known as shooting stars.

  • Some meteors are very large and they reach the Earth before they evaporate completely.

  • The meteor that reaches the Earth is known as meteorite.