An ergodic family: one computes: As is irrational, the action of the translations on the unit circle is ergodic. Consequences: The spectrum of does not depend on . (Pastur) The absolutely continuous spectrum does not depend on . (Last-Simon) There is no discrete spectrum. (Pastur) The Lyapunov exponent exists almost surely The absolutely continuous spectrum is the essential closure of the set of energies where the Lyapunov exponent vanishes (Ishii - Pastur - Kotani). Almost sure existence of the density of states (it is the harmonic conjugate of the Lyapunov exponent - Thouless formula). The spectrum is the set of growth point of the integrated density of states.