Red+Shift

=__﻿Red Shift__ = __the wavelength of the light is stretched, so the light is seen as '//shifted//' towards the red part of the spectrum.__  We now know that most other galaxies are moving away from us. This means that light from these galaxies is shifted to longer. It is also getting redder - in other words, it is 'red-shifted'.



 You may heard the increased pitch of an approaching police siren and the sharp decrease in pitch as the siren passes by and goes. The effect occurs because the sound waves arrive at the listener's ear closer together as the source approaches, and further apart as it goes. In every case, there is an audible change in pitch as the source approaches and then passes an observer. Different types of redshifts have different causes.
 * The **Doppler Redshift**. If the source of light is moving away from you then the wavelength of the light is stretched out, i.e, the light is shifted towards the red. Individually, they are called blueshifts and redshifts. Together, they are known as doppler shifts.


 * The **Cosmological Redshift** is a redshift caused by the expansion of space. The wavelength of light increases as it passes through the expanding universe between its point of emission and its point of detection by the same amount that space has expanded during the crossing time.


 * The **Gravitational Redshift** shifts the frequency of a photon lower energy when it climbs out of a gravitational field.

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