Red Shift
This lesson covers:
- How to interpret red-shift in absorption spectra
- How we know that other galaxies are moving away from us
- The big bang theory of the origin of the universe
Tip
'Red shift', 'Red-shift' and 'Redshift' all mean the same thing. We have tended to use 'Red-shift' in this lesson but you should get marks for any of the three.
Cosmic microwave background radiation (CMBR)
Cosmic microwave background radiation (CMBR) is electromagnetic radiation that is observed in all directions.
Initially radiation from the big bang was incredibly hot.
As the universe has expanded and cooled, the background radiation has dropped in frequency.
Red shift equation
The redshift equation allows us to calculate the recessional velocity of a galaxy based on the observed shift in wavelength of light from that galaxy.
Where:
- Δλ = the difference between the observed wavelength and the original wavelength. It is the amount that the wavelength has been shifted.
- λ is the original wavelength of light.
- v = recessional velocity of the galaxy.
- c = speed of light in a vacuum, 300,000,000 m/s.
Worked example: Calculating recessional velocity
An astronomer records the redshifted wavelength of a galaxy to be 525 nm. The original wavelength of the light is 500 nm.
Calculate the recessional velocity of the galaxy.
Which side of the absorption spectra above has the longer wavelength?
The red side on the left
The violet side on the right
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extra / missing / wavelengths / reflected / absorbed
- A star emits light of all wavelengths.
- However, some of light are by chemicals in the star's atmosphere.
- Therefore, light that reaches the earth has some wavelengths of light .
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Which of these provides evidence for the Big Bang?
Doppler effect
Red-shift
Blue-shift
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Red-shift is when light from distant galaxies show an absorption spectra pattern that has been shifted to:
The violet side of the spectra
The red side of the spectra
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How many galaxies show a red-shift?
None
Nearly all
Only a few
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smaller / larger / decrease / increase / towards / away
Red-shift occurs because the light emitted by an object moving from us will be stretched. The stretching causes the light's wavelength to . The faster an object moves away from us, the the red shift.
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Which is the correct explanation for why galaxies are moving away from each other?
Galaxies are moving away from each other by travelling through space
Space and the universe itself is expanding and this makes galaxies further apart
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What is the basic idea of the Big Bang theory?
The Universe expanded from a single tiny point of high density and pressure
The Universe will end in a cold expanse of darkness
Two black holes merged to create the universe
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Give one strength and one weakness of the balloon model in representing the idea of an expanding Universe.
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Why do we believe in the big bang theory?
universe / contracting / expanding / red-shift / away / bang
- Light that reaches earth from other galaxies shows , and the further away the galaxy the more red-shifted its light is.
- This suggests that all galaxies are both moving away from us, and moving from each other.
- This suggests that the whole universe is .
- If we extrapolate further and further back in time, it implies that the universe must have been smaller in the past.
- Ultimately, it's believed the universe started from a single point which had all of the mass and energy of the contained in that point.
- The expansion of the universe from this initial small point is called the big and started about 13.8 billion years ago.
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Why do scientists believe in the Big Bang theory?
Its predictions are supported by observations
It feels right
It was the first scientific idea to explain the beginning of the Universe
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