= Quasar-cloud redshift separation
{title2=$d_{\rm proper}\simeq c\,\delta z/[(1+z)H(z)]$}
For nearby <redshifts> in a homogeneous expanding universe, the <comoving radial distance> increment is $c\,\delta z/H(z)$. Multiplying by the <scale factor> at the absorber's epoch gives the displayed <proper distance in cosmology>. The conversion neglects <peculiar velocities>; observed <redshift> differences can also contain such <velocities> and errors in the <quasar> emission <redshift>.
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