  We investigate the power of spectral synthesis as a mean to estimate physical
properties of galaxies. Spectral synthesis is nothing more than the
decomposition of an observed spectrum in terms of a superposition of a base of
simple stellar populations of various ages and metallicities (here from Bruzual
& Charlot 2003), producing as output the star-formation and chemical histories
of a galaxy, its extinction and velocity dispersion. We discuss the reliability
of this approach and apply it to a volume limited sample of 50362 galaxies from
the SDSS Data Release 2, producing a catalog of stellar population properties.
A comparison with recent estimates of both observed and physical properties of
these galaxies obtained by other groups shows good qualitative and quantitative
agreement, despite substantial differences in the method of analysis. The
confidence in the method is further strengthened by several empirical and
astrophysically reasonable correlations between synthesis results and
independent quantities. For instance, we report the existence of strong
correlations between stellar and nebular metallicites, stellar and nebular
extinctions, mean stellar age and equivalent width of Halpha and 4000 \AA
break, and between stellar mass and velocity dispersion. We also present
preliminary results of an analysis of a magnitude-limited sample which clearly
reveals that the bimodality of galaxy populations is present in the parameters
computed in the synthesis. Our results are also consistent with the
"down-sizing" scenario of galaxy formation and evolution. Finally, we point out
one of the major problems facing spectral synthesis of early-type systems: the
spectral base adopted here is based on solar-scaled evolutionary tracks whose
abundance pattern may not be appropriate for this type of galaxy.
