It occurs when electromagnetic radiation, usually in the form of visible light, that is emitted from an object is shifted toward the red end of the spectrum. The wavelength, in a sense, is increased in red shift. The red shift is considered the opposite of the blue shift. Red shift can occur at any wavelength and be called red shift, even if the waves are technically longer than the color red.

An observed red shift within the universe occurs when distant galaxies, quasars, and intergalactic gas clouds increase in proportion to their distance from the earth. The mechanism of the red shift is the Big Bang model of physical cosmology.

Gravitational red shift is observed if the receiver is located at a greater gravitational potential from the source. The cause of the gravitational red shift is the dilation of time that occurs near huge objects, according to general relativity.

See also

• Astronomical red shift
• Extragalactic red shift Observations

In nearby objects, within the Milky Way galaxy, observed red shifts are related to the line of site velocities associated with the objects being observed. Such observations of red and blue shifts have enable astronomers to measure relative velocities of objects orbiting the stars in the Milky Way galaxy. Small shifts around individual stars allow astronomers to diagnose and measure the presence of and characteristics of planets around the stars.

Measurements of red shifts in fine detail are used in helioseismology to determine the precise movements of the photosphere of the sun.

Red shifts have laso been used to make measurements of the rotation rates of the planets.

The very bright quasars were the first of the “high-red shift” extragalactic features. According to Hubble’s Law, the degree of red shift is proportional to the galaxy’s distance from earth.