Spectroscopy of galaxies in Abell 370: a study of the cluster content.

After a brief review of the observations of distant clusters of galaxies (z ≥ 0.2) and the evolutionary effects already detected, the author presents the data obtained on the cluster Abell 370 (z = 0.37), both with photometry and spectroscopy. A first analysis leads to the conclusion that the cluster content is different than the one expected for a rich cluster and that 50% of spiral-like galaxies are identified. An interpretation in terms of burst of star formation is proposed for the blue galaxy excess detected in Abell 370.