Doppler Effect

The Doppler effect can be "felt" when a car drives past you. It sounds like it's getting louder - then it passes you and it sounds just different - you may have expected it to get softer - but it doesn't - the sound completely changes. The noise coming from the car never changed - and you never changed but the distance between the car and you changed.

This is my favorite illustration - the car continues to emit its sound in the form of waves but depending on where the observer or person is standing - they are effected by either looooooong waves that don't come very often (aka low frequency) or short waves that come often (high frequency).

This next illustration adds in the fact that if the object and the observer are stationary - then the wave lengths are not close together and not long wavelength - they are just right. But when the object moves closer to the observer - the waves are more bunched up so there is a smaller wavelength and a higher frequency (number of waves coming at ya!) - the result is that your ear hears a higher pitch. Then the object moves away sending long wavelengths and lower frequencies (fewer waves) and you hear a lower pitch.

Pitch:

This also explains the blue shift - red shift phenomenon. When the wavelengths are short and the frequency is high and thus the pitch to your ears is high - then the light that you see through your eyes is blue. (blue shift)

But when the wavelengths are long, the frequency is low and the pitch is low to your ears - then the light you see through your eyes is red. (red shift)

So - let's use this when determining how a star is moving. When you take your samples and you find that the absorption lines are moving - either towards the red or the blue. If its blue - then the celestial object is moving towards you - if it's red than the celestial object is moving away.

This is a red shift - the absorption lines are moving in the red direction between the two samples.

Experiments:

1. make a recording of your own doppler effect!