Why light from distant galaxies is shifted towards red, why more distant galaxies move away faster, and how this, with the cosmic microwave background, supports the Big Bang theory.
What you will learn
- Explain what red-shift is and what it tells us about a galaxy
- Use speed and distance data for galaxies, including the gradient of a graph (Higher)
- Explain how red-shift supports the Big Bang theory and an expanding universe
Stretched light
Hydrogen and other elements absorb light at exact wavelengths, so a spectrum has dark lines in a pattern astronomers know from the laboratory.
In light from distant galaxies the same pattern appears, but moved towards the red (longer wavelength) end.
This red-shift is an increase in the observed wavelength. It means the galaxy is moving away from us: the waves are stretched out. The speed of light does not change, so a longer wavelength means a lower frequency.
The rest of this lesson and its 10 practice questions are locked.
In this lesson
- Stretched light
- Further means faster
- The Big Bang
- Try it: Read the spectra
10 practice questions, marked as you go; about 25 minutes in all.
Key terms
Red-shift, Moving away, Big Bang theory, Steady State
In this unit: Space physics
The solar system and the Milky Way, the life cycle of a star, orbits and orbital speed, red-shift and the expanding universe, and what is still unknown.