Red-Shift & Light from Galaxies
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20 Terms
What is red-shift?
An increase in the wavelength of light received from a distant object.
Why is it called red-shift?
The wavelengths shift towards the red end of the visible spectrum.
What happens to the frequency of light when it is red-shifted?
Its frequency decreases.
What happens to the wavelength of light when it is red-shifted?
Its wavelength increases.
What does red-shift tell us about most distant galaxies?
They are generally moving away from us.
What happens to light from a galaxy moving away from an observer?
Its wavelength is stretched, producing red-shift.
What is blue-shift?
A decrease in the wavelength of light received from an approaching object.
What happens to the frequency of blue-shifted light?
It increases.
What does blue-shift indicate about an object's motion?
It is generally moving towards the observer.
How can astronomers detect red-shift?
By comparing the positions of spectral lines from distant galaxies with their known positions in laboratory spectra.
What are spectral lines?
Distinctive wavelengths absorbed or emitted by atoms and other particles.
Why are spectral lines useful for studying galaxies?
They allow astronomers to identify elements and measure wavelength shifts.
What happens to spectral lines when light is red-shifted?
They move towards longer wavelengths.
What happens to spectral lines when light is blue-shifted?
They move towards shorter wavelengths.
What does a larger red-shift generally indicate?
A greater recession speed, for the relatively nearby galaxies described by the simple Doppler model.
What is the relationship between a galaxy's distance and its red-shift?
More distant galaxies generally show a greater red-shift.
What does the red-shift of distant galaxies suggest about the Universe?
The Universe is expanding.
Why is red-shift important evidence in astronomy?
It provides evidence that most distant galaxies are receding and space is expanding.
Do all galaxies show red-shift?
No, some nearby galaxies show blue-shift because of their motion towards us.
Why is the red-shift of distant galaxies not simply explained by every galaxy moving through static space?
On cosmological scales, the observed red-shift is primarily associated with the expansion of space itself.