The Solar System (Cambridge O Level Physics)

• The Solar System consists of:
  1. The Sun
  2. Eight planets
  3. Natural and artificial satellites
  4. Dwarf planets
  5. Asteroids and comets

Objects in the Solar System

The Solar System contains a star (the Sun), 8 planets, minor planets, moons and other smaller bodies

The Sun & the Planets

• The Sun lies at the centre of the Solar System
  • The Sun is a star that makes up over 99% of the mass of the solar system

• There are eight planets and an unknown number of dwarf planets which orbit the Sun
  • The gravitational field around planets is strong enough to have pulled in all nearby objects with the exception of natural satellites
  • The gravitational field around a dwarf planet is not strong enough to have pulled in nearby objects

• The 8 planets in our Solar System in ascending order of the distance from the Sun are:
  • Mercury
  • Venus
  • Earth
  • Mars
  • Jupiter
  • Saturn
  • Uranus
  • Neptune

Satellites

• There are two types of satellite:
  • Natural
  • Artificial

• Some planets have moons which orbit them
  • Moons are an example of natural satellites

• Artificial satellites are man-made and can orbit any object in space
  • The International Space Station (ISS) orbits the Earth and is an example of an artificial satellite

Asteroids & Comets

• Asteroids and comets also orbit the sun
• An asteroid is a small rocky object which orbits the Sun
  • The asteroid belt lies between Mars and Jupiter

• Comets are made of dust and ice and orbit the Sun in a different orbit to those of planets
  • The ice melts when the comet approaches the Sun and forms the comet’s tail

• The planets and moons of the Solar System are visible from Earth when they reflect light from the Sun
  • The outer regions of the Solar System are around 5 × 10¹² m from the Sun, which means even light takes some time to travel these distances
• The light we receive on Earth from the Sun takes 8 minutes to reach us
  • The nearest star to us after the Sun is so far away that light from it takes 4 years to reach us
  • The Milky Way galaxy contains billions of stars, huge distances away, with the light taking even longer to be seen from Earth

• The speed of light, equal to 3 × 10⁸ m/s, is constant everywhere in the Universe
• The time taken to travel a certain distance in the Solar System can be calculated by using the equation:

• And rearranging it for time: