Per-direction mean of the MASSCW priors at observing frequency ν_obs = 150 MHz, exhibiting less variability than the single realisation of Figs. 8a,b (note the smaller colour ranges). Three famous galaxy clusters stand out; these are (in increasing order of declination) the Hercules Cluster, the Coma Cluster, and Abell 2199. Top: specific intensity mean. Bottom: specific-intensity–weighted mean (cosmological) redshift mean.