BIO Space Sciences
In our expanding universe, galaxies are rushing away from us at vast speeds. Nearby galaxies, only millions of light years from Earth, are speeding away at hundreds of kilometres every second. More distant galaxies, billions of light years away, are rushing away at speeds in excess of 100,000 kilometres every second.
A natural consequence of this rapid expansion is the stretching of light via the Doppler Effect.
This stretching of light is similar to the stretching of sound waves here on Earth. The pitch of the sound from a motorcycle is lowered as it moves away from you. Just as sound waves are stretched (lower pitch) as a motorcycle races away, the light waves are stretched (redder light) as a distant galaxy races away.
When we look at distant galaxies, we are looking into the past, as light can take billions of years to travel across the universe. This presents an opportunity for astronomers to directly observe the ancient universe.