We report observations of two nearby Type Ia supernovae ( SNe Ia ) for which observations of Cepheid variables in the host galaxies have been obtained with the Hubble Space Telescope : SN 1994ae in NGC 3370 and SN 1998aq in NGC 3982 .
For NCG 3370 , we used the Advanced Camera for Surveys to observe 64 Cepheids that yield a distance of 29 Mpc , the farthest direct measurement of Cepheids .
We have measured emission lines from H II regions in both host galaxies which provide metallicity-dependent corrections to their period-luminosity relations .
These two SNe Ia double the sample of “ ideal ” luminosity calibrators : objects with well-observed and well-calibrated light curves of typical shape and with low reddening .
By comparing them to all similarly well-measured SNe Ia in the Hubble flow , we find that H _ { 0 } = 73 \pm 4 ( statistical ) \pm 5 ( systematic ) km s ^ { -1 } Mpc ^ { -1 } .
A detailed analysis demonstrates that most of the past disagreement over the value of H _ { 0 } as determined from SNe Ia is abated by the replacement of past , problematic data by more accurate and precise , modern data .