Physics - Waves from Space

The light and heat from the Sun takes just over 8 minutes to reach the Earth so if the sun was to somehow be extinguished we on Earth would not find out until 8 minutes later. Light from the stars takes even longer. The closest star to our Solar System is Proxima Centauri - light takes just over 4 years to reach us from this star. When astronomers look at the most distant galaxies, they are seeing them as they were thousands of millions of years in the past.

So how can astronomers study the Universe using these waves from space? There are many advanced techniques but one of the fundamental ones is to use the Doppler effect. If a wave source is moving relative to an observer there will be a change in the observed wavelength and frequency. You can hear this when you are standing next to a highway with fast moving traffic. As the vehicles approach, they sound slightly different to when they are moving away. The pitch of the sound is higher as they approach because the waves are 'bunched up'. This shortens their wavelength and increases their frequency so they sound higher pitched than they do when they are not moving. As the vehicle passes and moves away, the waves get left behind and their wavelength is longer and their frequency is lower.

This happens with light too but is only detectable if something is moving at high speed as light waves have such a high velocity. Shorter wavelengths of light are bluer and longer ones are redder. Astronomers studying distant galaxies have observed an increase in the wavelength of light from most of them. The further away the galaxies are, the bigger the observed increase in wavelength. This effect is called red-shift and shows that the most distant galaxies are moving away from us at the fastest rates - the Universe is expanding.

Microwaves have played an important part in understanding the formation of the Universe. Cosmic microwave background radiation (CMBR) is a form of electromagnetic radiation filling the Universe. It comes from radiation that was present shortly after the big bang that has been cooling ever since. The ‘Big Bang’ theory is currently the only theory that can explain the existence of CMBR but who knows, tomorrow, or a hundred years from now, there could be new discoveries that change our understanding completely.