Galaxies, redshift and the Big Bang Cambridge IGCSE Physics (9–1) revision
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In plain words
Our Sun is one of billions of stars in the Milky Way galaxy, and there are billions of galaxies. Light from distant galaxies arrives stretched towards the red end of the spectrum (redshift), which tells us they are moving away. The further off they are, the faster they go. Run that backwards and everything started together: the Big Bang.
Three things to know
- The Sun is one of billions of stars in the Milky Way galaxy, and the Universe contains billions of galaxies. A light-year is the distance light travels in a year.
- Light from distant galaxies is redshifted: its wavelength is stretched because they are moving away. The further away a galaxy is, the faster it is moving.
- So the Universe is expanding, which supports the Big Bang theory: it began from a single very hot, dense point. The cosmic microwave background radiation is more evidence.
Tips and tricks
- Give the whole chain for full marks: redshift → galaxies are moving away → the Universe is expanding → this supports the Big Bang.
- A light-year is a distance, not a time.
It lands in your notebook with its questions as flashcards.
Galaxies, redshift and the Big Bang: 6 questions and answers
These are the quiz’s questions. Do the quiz first, then come back here for the ones that got you.
What is a galaxy?
The Milky Way is a galaxy of billions of stars.
What does redshift tell us about a galaxy?
The light waves are stretched as the galaxy recedes.
What is a light-year?
It is a unit of distance.
Which is evidence for the Big Bang?
It shows the Universe is expanding from an earlier, denser state.
How does the redshift of a galaxy change with its distance from us?
The further away a galaxy is, the faster it is moving away.
Which galaxy is the Solar System in?
The Sun is one of the billions of stars in the Milky Way.
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Worksheet
4 questions, 9 marks. Write your answers on paper, then check them.
Galaxies, redshift and the Big Bang
Cambridge IGCSE Physics (9–1) 0972 · 9 marks · papermunch.org
Name ______________________________ Date ______________
State what is meant by redshift.[2]
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The light from a galaxy moving away has its wavelength increased, shifted towards the red end of the spectrum.
Explain how redshift supports the Big Bang theory.[3]
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Almost all galaxies show redshift, and more distant ones show more, so the Universe is expanding. Running that backwards, everything began in one place.
State what is meant by a light-year.[2]
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The distance travelled by light (in a vacuum) in one year.
Name the radiation, coming from every direction in space, that is evidence for the Big Bang, and state where it came from.[2]
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Cosmic microwave background radiation. It is radiation left over from the early, hot Universe, stretched to microwave wavelengths by the expansion.
Answers: Galaxies, redshift and the Big Bang
- 1. The light from a galaxy moving away has its wavelength increased, shifted towards the red end of the spectrum.
- 2. Almost all galaxies show redshift, and more distant ones show more, so the Universe is expanding. Running that backwards, everything began in one place.
- 3. The distance travelled by light (in a vacuum) in one year.
- 4. Cosmic microwave background radiation. It is radiation left over from the early, hot Universe, stretched to microwave wavelengths by the expansion.