Compton scattering of the Cosmic Microwave Background Radiation (CMBR) photons hit the gas cloud surrounding a galaxy and collide with electrons and scatter to different wavelengths. As a result, the intensity of the CMBR is depleted in the direction of the cluster. The depletion is directly proportional to the depth of the cloud. If the depth of the cloud is equal to the width of the cloud, the angular width can be measured. For example, if the cloud has a diameter of 5 x 106 LY and subtends 0.0300, then the galaxy must be 10 x 106 LY away.

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