Let us say that I am speaking to you, then I am the source and you are the detector.
Now if I am moving while speaking, then the waves that I emit will have an extra added velocity as they move towards you. As a result, you can think that the waves become squished together and thus the perceived wavelength will be smaller and the frequency will appear larger than that emitted by the source.
Now if I am moving while speaking, then the waves that I emit will have an extra added velocity as they move towards you. As a result, you can think that the waves become squished together and thus the perceived wavelength will be smaller and the frequency will appear larger than that emitted by the source.
This is the case with ambulances or fire trucks as they comes closer, the pitch increases and as they are leaving you, the sound becomes deeper.
With stars, astronomers observed that the stars' colors varied and thought it was solely due to their temperature. However, it was shown that the color changes were due to the fact that the stars were either moving further away or closer to the Earth. If they were moving closer to us, they would be 'blueshifted'. If they were moving further away, they would be 'redshifted.'
It is denoted that way because blue light waves have longer wavelengths than red light waves.
You can find alot of information on Wikipedia .
https://en.wikipedia.org/wiki/Redshift
I hope this helps clarify the Doppler effect. Let me know if you need further assistance. :)
