In order to determine if a cosmological object is Doppler shifted, the light from the source is directed to a spectrograph. We can determine which elements are present in an “object” by measuring the position of the spectral lines in the graph. The wavelength emitted by an element is determined by the excitation states of atoms and manifests as emission lines or absorption lines in a device known as a spectrograph. Using experiments here on earth, we discovered that each element in the periodic table emits light at different wavelengths. Blue shift is analogous to the pitch going up, and red shift is analogous to the pitch going down. In the domain of light, when an object is moving toward an observer, the light it emits will appear blue-shifted to the observer, but when the object is moving away from the observer, the light will appear red-shifted. In the domain of sound, when an object is moving toward an observer, the sound it emits will have a higher pitch as heard by the observer, and when an object is moving away from the observer, a lower pitch will be heard. The effect was originally applied to sound waves but this can be applied to any wave phenomenon, including light. The Doppler Effect, or Doppler shift, corresponds to a shift in frequency of a wave relative to an observer moving relative to the source of the wave. The Doppler effect is named after Christian Doppler, an Austrian physicist, who described this effect in 1842. Well, that is known as the “Doppler Shift” and has everything to do with the idea that the universe is “supposedly” expanding because of the “Doppler Effect” for light called the “red shift”. Most people can even imitate that sound themselves. You notice that the sound of the siren changes pitch. Ok, we are all familiar with this situation: you hear an siren on a firetruck, ambulance, or police car and you stop for it to pass.
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