The Solar System (AQA GCSE Physics)

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

• There are 8 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
  • There are 4 rocky planets: Mercury, Venus, Earth and Mars
  • There are 4 gas planets: Jupiter, Saturn, Uranus and Neptune

• 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 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 objects in our solar system

• Our solar system is just one small part of the Milky Way galaxy
• There are billions of stars in the Milky Way galaxy
• Some of these stars also have planets which orbit them
• The Universe is made up of many different galaxies

Our solar system is just one out of potentially billions in our galactic neighbourhood, the Milky Way. There are estimated to be more than 100 billion galaxies in the entire universe

Distances between Planets in the Solar System

• 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 is a constant 3 × 10⁸ m/s
  • Therefore, using the equation:

• • The time taken to travel a certain distance can be calculated by rearranging to:

Step 1: State the equation for the time taken for light to travel a certain distance

Step 2: Substitute in the values

• • The distance travelled is the radius of the orbit
    • Distance, d = 5.8 × 10⁹ m.
  • Speed = the speed of light, v = 3.0 × 10⁸ m/s

Step 3: Round up the answer and include units