Astrophysics (index)about

Alcock-Paczyński Effect

(distortion of the apparent size of galaxy clusters)

The Alcock-Paczyński Effect is an illusion affecting the determination of the depth of Galaxy Clusters: if Gravity is pulling the nearest and furthest galaxies inward, then their relative Redshift will be less than suggested by the actual depth, or conversely, the actual depth of the galaxy cluster will be greater than suggested by the relative redshift.

The Alcock-Paczyński Test is a method of determining the geometry of the universe (e.g., the Hubble Constant) despite this effect, by adjusting results using structures that are known to be circular or spherical, i.e., where it can be seen how to compensate for the illusion.


Referenced by:
Redshift Space