1987A: The greatest supernova since Kepler

After a period of initial confusion, we now seem to understand in some detail why a star like Sanduleak -69° 202 gave rise to a supernova like 1987A. The detection of the neutrino burst produced at core collapse has confirmed basic ideas of Type-II supernova causality and energetics (without being able to distinguish prompt from delayed shock ejection). Constraints on the nature of the neutrinos themselves confirm or extend laboratory limits on, and conventional theory for, rest mass, magnetic moment, etc. The unusual early light curve and spectra turn out to be a natural result of core collapse when the star was compact and blue, after passing through a red, extended phase (confirmed by evidence for mixing and mass loss characteristic of red supergiants). Synthesis of about $0.07M_{\odot }$ of ${\mathrm{Ni}}^{56}$ (as was previously suspected in SNII's with exponentially tailed light curves) has been revealed by a similar light curve and by an infrared line, gamma rays, and hard x rays, all widely believed to reflect the presence and decay of ${\mathrm{Ni}}^{56}$ to ${\mathrm{Co}}^{56}$ to ${\mathrm{Fe}}^{56}$. A number of puzzles remain concerning unexpected variable soft-x-ray emission, a possible speckle companion, and evidence for extensive mixing, fragmentation, and filamentation. Most of the lessons still to be learned from 1987A probably pertain to the detailed (three-dimensional) structure and composition of evolved massive stars rather than to the basic physics of Type-II supernovae.