SN 1987A was a type II supernova in the Large Magellanic Cloud, a dwarf satellite galaxy of the Milky Way. It occurred approximately 51.4 kiloparsecs (168,000 light-years) from Earth and was the closest observed supernova since Kepler's Supernova. 1987A's light reached Earth on February 23, 1987, and as the earliest supernova discovered that year, was labeled "1987A". Its brightness peaked in May, with an apparent magnitude of about 3.

It was the first supernova that modern astronomers were able to study in great detail, and its observations have provided much insight into core-collapse supernovae.

SN 1987A provided the first opportunity to confirm by direct observation the radioactive source of the energy for visible light emissions, by detecting predicted gamma-ray line radiation from two of its abundant radioactive nuclei. This proved the radioactive nature of the long-duration post-explosion glow of supernovae.

For over thirty years, the expected collapsed neutron star could not be found, but in 2019, indirect evidence for its presence was found with the Atacama Large Millimeter Array telescope, with further evidence found in 2021 using the Chandra and NuSTAR X-ray telescopes.