Solar system

Physics - The Solar System

Introduction

• 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.’

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.