Redshift
= Redshift
{title2=
$1+z=
u_{
m em}/
u_{
m rec}$
}
The <redshift> $z$ compares emitted and received local <frequencies> or <wavelengths>: $1+z=\lambda_{\rm rec}/\lambda_{\rm em}=\nu_{\rm em}/\nu_{\rm rec}$. Motion, gravitation, and cosmological expansion can all contribute.