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The Doppler Effect
When astronomers look at the spectra of stars in distant galaxies, they found that the
spectra looked similar from the stars of our own galaxy. However the spectra was
shifted slightly by the same (relative) amount toward the red end of the spectrum. In other
words the wavelength was slightly longer that it should've been. This was called red shift,
since the spectra from the galaxies had `shifted' into the more red end of the spectrum.
This shift was caused by the motion of the stars and our planet. We are moving away
from them, while they move away from us, so in effect the wavelength gets stretched.
This is called the doppler effect. The same can be said for galaxies moving closer to us.
Their spectra is shifted into the more blue spectrum, creating what is known as blue shift.
This is where the wavelength is squashed. Using the known of blue shift and red shift,
scientists can work out the origins of our universe. Most galaxies seem to be moving
away from us, and in 1929 this idea led
Hubble to publish findings that the size of a galaxies red shift if proportional to it's
distance from us. The further away the galaxy was, the faster it was moving. This
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So where can we see the doppler effect in every day life? As Sheldon tells us in big
bang theory `It's the apparent change in the frequency of a wave caused by relative
motion between the source of the wave and the observer.' So for example, when a police
car drives past with their sirens on, the pitch of the siren seems to become high just as it
passes us and then it seems to become lower as it travels away from us.…read more