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What is the meaning behind the terms red-shift and blue-shift?

Whitney Matthews

in Homework Help

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Kristi Hammond on April 26, 2019

Red shift and blue shift refers to the light each time more reddish or more bluish. A useful analogy is the Doppler effect with the sound. The sounds of an approaching police car has a higher pitch than normal, while if it is far away from the pitch would be lower. Objects that make noise and are moving toward you make a loud sounds, and objects that are moving away from it to do the lower-pitched noise. The same thing happens with the light; moving objects to appear more blue (and are referred to as having been blue-shifted) and those moving objects are more reddish. We are not aware of this in normal life due to the speed of light is enormous, and only the objects that are moving away or toward you with a negligible fraction of this speed have been significant blue or red shift. It is important to note that there is a difference with the red shift usually used by cosmologists. They often specify the distance to a very distant galaxy by its red shift. This can be done by the Hubble Law, which says that the more distant a galaxy is, the faster away from us (and therefore the more red shifted it is). Hubble's Law, therefore, provides a way to relate red shift to distance. The most important difference is the cause of the red shift. While it is true that a distant galaxy can be moving away from us, it is just as likely to move towards us (and therefore appear blue shifted). However, the main cause of the red shift cosmological expansion of the Universe! As the light travels towards us, space itself is stretched by the expansion of the Universe and the wavelength of the light is stretched due to this. The wavelength of the light increases, which also causes the displacement to the red one (since red has a longer wavelength than blue light, for example). The longer light travelled (i.e., more than the galaxy distance), the more this happens, so the more red shifted and we recover the Law of Hubble.


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