Dark matter was postulated by Jan Oort in 1932 , albeit based upon flawed or inadequate evidence , to account for the orbital velocities of stars in the Milky Way , and by Fritz Zwicky in 1933 to account for evidence of `` missing mass '' in the orbital velocities of galaxies in clusters .
Dark matter was first proposed by Jan Oort in 1932 to account for the orbital velocities of stars in the Milky Way . Fritz Zwicky in 1933 used it to account for evidence of `` missing mass '' in the orbital velocities of galaxies in clusters .