Typical novae occur when (a) a red-giant star ejects a planetary nebula; (b) two neutron stars merge, forming a more massive neutron star; (c) an extremely massive star collapses, and also ejects its outer atmosphere; (d) matter accreted from a companion star unstably ignites on the surface of a white dwarf; or (e) a neutron star’s magnetic field becomes strong enough to produce two oppositely directed jets of rapidly moving particles.