einstein

* If the source of sound is rushing toward you, the waves will not get to you any faster. However, in what is known as the Doppler effect, the
waves will be compressed and the interval between them will be smaller. The decreased wavelength means a higher frequency, which
results in a higher-pitched sound (or a lower one, when the siren passes by and starts moving away). A similar effect happens with light. If
the source is moving toward you, the wavelength decreases (and frequency increases) so it is shifted to the blue end of the spectrum. Light
from a source moving away will be red-shifted.