  We have studied the influence of the presupernova structure and the degree of
Ni-56 mixing on the bolometric light curve of SN 1987A in terms of radiation
hydrodynamics in the one-group approximation by abandoning LTE and by taking
into account nonthermal ionization and the contribution of spectral lines to
opacity. Our study shows that moderate Ni-56 mixing at velocities of < 2500
km/s can explain the observed light curve if the density of the outer layers of
the presupernova exceeds the value obtained in the evolutionary model of a
single nonrotating star severalfold. Abandoning LTE and allowing for nonthermal
ionization when solving the equation of state and calculating the mean
opacities and the thermal emission coefficient leads to a significant
difference between the gas temperature and the radiation temperature in the
optically thin layers of the supernova envelope. We demonstrate the fundamental
role of the contribution of spectral lines to the opacity in an expanding
envelope and of the accurate description of radiative transfer in reproducing
the observed shape of the bolometric light curve. We have found that
disregarding the contribution of spectral lines to the opacity introduces an
error of 20% into the explosion energy, and that a similar error is possible
when determining the mass of the ejected matter. The resonant scattering of
radiation in numerous lines accelerates the outer layers to velocities of 36
000 km/s; this additional acceleration affects the outer layers with a mass of
10^{-6} Msun. Proper calculations of the supernova luminosity require that not
only the delay effects, but also the limb-darkening effects be taken into
account.
