Redshift

Redshift is a measure of the displacement of spectral lines to longer wavelengths in the electromagnetic spectrum. It is caused by the Doppler effect and is a function of the speed at which an object is moving away from an observer. The redshift of an object increases as its distance from the observer increases.

The most common type of redshift is that caused by the motion of objects in our universe away from us. This cosmological redshift was first predicted by Georges Lemaître in 1927 and later observed by Edwin Hubble. The amount of redshift depends on the speed at which an object is moving away from us, with more distant objects moving faster and therefore exhibiting greater redshifts.

There are two other types of redshift that can occur. One is due to gravitational effects, where light traveling through a gravitational field experiences a shift to longer wavelengths (gravitational redshift). The other occurs when light passes through a medium with a different refractive index than vacuum (refractive index dispersion), resulting in a wavelength-dependent shift (dispersive or chromatic redshift).

Redshifts can be measured using spectroscopy, where the wavelength shifts of spectral lines are determined from their position relative to known reference lines. By measuring the amount of shift, one can determine the velocity at which an object is receding along our line-of-sight. Redshifts have been used to study everything from nearby stars to galaxies billions of light years away and have played a key role in our understanding of cosmology and the expansion of our universe.