λ_{obs} = λ_{source} \begin{matrix}√ & \overline{1 + β} \\ √ & \overline{1 − β} \end{matrix}

λ_{obs} ≃ λ_{source} (1 + β)

velocity (km/s) = H distance (Mpc)

z = \frac{λ_{obs}}{λ_{source}} − 1