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| (3-21-17.) Let's look a little closer at exactly what we mean when we refer to Doppler shift. Any transmitted signal, whether it be man-made or a natural emission from a star, has a certain frequency characteristic. We don't really care what frequency it is, or even if it carries intelligent information on it, just its basic frequency. When this signal strikes any object that is moving, it experiences what we call compression or rarefaction. Compression is like when we compress air into a tank. The tank is a fixed volume so at ambient pressures the air molecules inside the tank are spaced at the same distance as the air molecules outside the tank. When we pressurize the tank to, say, ten times the outside pressure, then for the same volume in the tank with ten times the air, the air molecules have to be closer together. That's how compression works. It puts more of anything in the same amount of space or distance. Rarefaction is the opposite of compression. Its more like letting the air out of a pressurized tank so that the air molecules are further apart in the tank. It puts less of anything in the same amount of space or distance. With our transmitted signal, if the object is moving toward the source of this signal, or if the source of the signal is moving toward the object, then the signal will experience compression as it reflects off of the object. That just means that the frequency increases as it is reflected off the surface of the moving object. That means that there will be more wavelengths in the same distance of measurement. This is referred to as 'blueshift'. However, if the object is moving away from the signal, then the reflected signal will experience rarefaction, meaning that the reflected signal decreases in frequency. This is referred to as 'redshift', meaning that the original signal has shifted down in frequency. If the original frequency was a green light transmission and the object was moving away from the signal source, then the signal would shift toward the red part of the spectrum, hence it would be 'redshifted'. It doesn't mean that the green light was turned into a red light, but only that the frequency of the signal that reflected off of the object is of a lower frequency and that lower frequency is dependent on the velocity of the object as it is moving away from the signal source. If this same green light transmission was to strike an object that was moving toward the signal, then the original green light transmission would be compressed, causing the same number of wavelengths to appear in a shorter space and the frequency of the reflected signal would increase, hence it would be 'blueshifted'. We illustrate this concept in the drawings below. To help you visualize these concepts a little better, we'll show our signal as a sinusoidal wave. This is the same kind of wave you see on oscilloscopes in movies, usually in science fiction movies. In the first drawing we show you our sinusoidal wave as a reference so you will understand what we mean. You'll have to imagine that this wave is moving from left to right. |
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| Questions or comments should be submitted to ncbonding@gmail.com. |
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| © 2017 |
| Author: Douglas Ray Lockwood |