Doppler EffectAnother thing that you can get from an absorption or emission spectrum is the velocity of the object producing the spectrum. This is due to the Doppler effect. This is the same effect you experience when an ambulance or a train passes by. The speed of the object affects the sound waves coming from it, so the sound of the ambulance or train whistle changes as it goes by. You could also get a similar effect if you are the one that is moving, and the sound source is stationary; basically, the sounds when you approach and recede are different.The same effect is seen in light waves, since light has wave-like properties (you didn't forget that, did you?). When an object is coming towards you, its light waves get squeezed in, causing the spectral features to shift to shorter wavelengths (be bluer than normal), while an object moving away would have its light stretched out and the spectral features would be shifted to longer wavelengths (be redder than normal). This situation is shown in Figure 10. In cases of
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