The Doppler Effect Flashcards
What is the Doppler Effect?
The change in the frequency and wavelength of a wave due to movement of its source
Why do the frequency and wavelength of a wave with a moving source change?
The waves bunch together in front of the source and stretch out behind it
What happens to the wavelength of a wave when the source moves away from you?
It increases
What happens to the frequency of a wave when the source moves away from you?
It becomes lower
For a light source moving away from you, the change in frequency and wavelength shifts light to which end of the spectrum?
Red end
“Red Shift”
Describe Red Shift
As a light source moves away from an observer, the wavelength increases and frequency lowers. This shifts the light towards the red end of the spectrum
What happens to the wavelength of a wave when the source moves towards you?
It decreases
What happens to the frequency of a wave when the source moves towards you?
It becomes higher
What colour will the light from a star moving away from us appear as more?
redder than the actual light emitted by the star
Describe Blue Shift
As a light source moves towards an observer, the wavelength decreases and frequency increases. This shifts the light towards the blue end of the spectrum
For a light source moving towards you, the change in frequency and wavelength shifts light to which end of the spectrum?
Blue end
“Blue Shift”
What colour will the light from a star moving towards us appear as more?
star will look bluer than it actually is.
What does the amount of red or blue shift depend on?
How fast the star is moving away or towards us.
Higher velocity means the waves are …. more
Higher velocity means waves are SHIFTED more
In the Doppler Shift formula, what does λ mean?
Emitted wavelength
In the Doppler Shift formula, what does f mean?
Emitted frequency
In the Doppler Shift formula, what does Δλ mean?
Difference between emitted wavelength and observed wavelength
In the Doppler Shift formula, what does Δf mean?
Difference between emitted frequency and observed frequency
In the Doppler Shift formula, what does v mean?
Recessional velocity
When is v positive and when is it negative?
Source moving away V is negative.
Source moving towards observer V is positive
When is Z negative
If red shift is negative = moving towards = blue shift
What is recessional velocity?
How fast the source is moving AWAY from the observer
What is red and blue shift called if the wavelength is not visible light?
Still red and blue shift
In the Doppler Shift formula, what does z mean?
The amount of Red/Blue Shift
What will happen to a radiation spectrum of a moving source if it is red-shifted?
What does it look like?
With absorption lines and a known frequency, how can you find redshift?
What is Δf?
Observed frequency - emitted frequency
When is Δf is negative and when is it positive?
With absorption lines and a known wavelength, how can you find redshift?
How to astronomers think red shift for all distant galaxies happens?
Cosmological red shift:
Space itself is expanding. Light waves are being stretched with it
What does HBB stand for?
Hot Big Bang Theory
What is the Hot Big Bang Theory?
The universe started off as an infinitely hot, infinitely dense singularity and has been expanding ever since
What evidence does the Doppler Effect give for the Hot Big Band Theory?
The spectra from galaxies all show Red Shift (the characteristic spectral lines of the elements are longer than expected), meaning they’re all moving apart.
Cosmologists don’t consider galaxies to be physically moving through space away from us. How do they explain Red Shift?
Space itself is expanding and waves are stretched with it.
What is the theory that space itself is expanding called, in relation to Red Shift?
Cosmological Red Shift
Why does the Red Shift of planets suggest that the universe started out as a single point?
The speed galaxies move away from us depends on how far away they are
What proportion of stars we observe are actually two stars orbiting each-other?
About half
How do we know that there are two stars when they are too far away to be resolved with telescopes?
Lines in their spectra show a binary star system
Two separate lines (one Blue Shift, one Red Shift)
What do we call a binary star system that has been identified by its line spectra?
Spectroscopic binary stars
How can the orbital period of a binary star system be calculated?
By observing how the absorption lines in the spectrum change with time
The time between maximum Blue Shift and maximum Red Shift
