The extragalactic distance scale

Cepheid variables are used to derive a Virgo cluster distance of 16.0+/-1.5 Mpc. In conjunction with the mean Coma radial velocity and the well-established Coma/Virgo distance ratio, this yields a Hubble parameter H-0=81+/-8 km s(-1) Mpc(-1). By combining this value with an age of the Universe greater than or similar to 16.8+/-2.1 Gyr that is derived from the metal-poor globular cluster M92, one obtains f(Omega,Lambda)greater than or similar to 1.39+/-0.22. This value is only marginally consistent with an Einstein-de Sitter universe with Omega=0 and Lambda=0, which has f=1. An Einstein-de Sitter universe with Omega=1 and Lambda=0, for which f=2/3, appears to be excluded at the 3 sigma level. It is shown that some recent small values of H-0 may have resulted from the large intrinsic dispersion in the linear diameters of galaxies, and from the fact that well-observed supernovae of Type Ia exhibit a luminosity range of similar to 20 at maximum light. A representative sample of recent estimates of H-0 is given in Table 1. The median value of the Hubble parameter from the data in this table is H-0 = 72 km s(-1) Mpc(-1), from which f(Omega,Lambda)greater than or similar to 1.24.