Position of First Doppler Peak

This talk describes an analytic calculation of the position of the first accoustic peak as a function of the matter density and the cosmological constant (work with Y.J. Ng and R. Rohm), agreeing with independent numerical studies. There is also discussion of supernovae observations and how together these approaches combine to suggest non-zero cosmological constant. An alternative to a constant vacuum density - quintessence - is mentioned.