3.3 m and from Type Ia Supernovae The use of type Ia supernovae
for measuring cosmological parameters is covered elsewhere in
this volume by Filippenko (nearby supernovae and determinations
of H0) and by Perlmutter (distant supernovae and m and ). Hence,
these objects will not be discussed in much detail here, except
to highlight their potential, and to summarize some of the main
difficulties associated with them so that they can be compared
relative to some of the other methods discussed in this review.
The obvious advantage of type Ia supernovae is the small
dispersion in the Hubble diagram, particularly after accounting
for differences in the overall shapes or slopes of the light
curves (Phillips 1993; Hamuy et al. 1995: Reiss, Press &
Kirshner 1997). In principle, separation of the effects of
deceleration or a potential non-zero cosmological constant is
straightforward, provided that (eventually) supernovae at
redshifts of order unity can be measured with sufficient signal-
to-noise and resolution against