where z is the redshift. D M is a factor that allows calculation of the comoving distance between two objects with the same redshift but at different positions of the sky; if the two objects are separated by an angle δ δ θ θ , the comoving distance between them would be D M δ δ θ θ . In a spatially flat universe, the comoving transverse distance D M is exactly equal to the radial comoving distance D C , i.e. the comoving distance from ourselves to the object.