(1) refining the cosmic distance scale by observing 18 spiral galaxies within 20 Mpc, searching for and measuring the periods and magnitudes of Cepheid variables, and

(2) calibrating the secondary distance indicators such as the Tully-Fisher relation for spirals, fundamental plane method for ellipticals, surface brightness fluctuation method and Type Ia supernovae.

The Hubble Constant and the Hubble Space Telescope Published in Suuri-Kagaku (Mathematical Science) in Japan, July 1997.

Observing the Expansion of the Universe using the Hubble Space Telescope Published in Illume magazine, October 1997.

* Calibration of the Tully-Fisher Relations*

The calibration of the Tully-Fisher (TF) relations and determining the H0 using these relations comprises the core of the Key Project. I have been leading an effort of calibrate both optical and IR TF relations and applying them to distant cluster samples to determine the H0. (A preprint will be ready *soon*, hopefully by the end of May!!)

John Huchra and Lucas Macri at Harvard-Smithsonian Center for Astrophysics
have obtained *BVRI* images of all of
the Key Project galaxies, and Lucas has recently finished the reduction
of these data, including performing surface photometry.
The figure below compares I-band and H-band TF relations *before (left)* and
*after* 1993, showing how much the HST observations helped in refining
the zero points of distance indicators. The H-band photometry
data are from the survey by Aaronson, Huchra and Mould (cf. Aaronson et al.
1980, ApJ).

*Hubble Constant*

We applied the I-band TF relation to the clusters of galaxies presented in Giovanelli et al. (1997 ApJ). The Hubble diagram is shown below. Averaging the H0's derived for five clusters with velocities 5000 km/s or larger, we obtain H0=73 km/s/Mpc.