Events detected by underground detectors on February 23, 1987

This report describes the principles of search for and detection of neutrino radiation from stars undergoing gravitational collapse. The authors describe the design and parameters of all underground neutrino detectors that were operational on February 23, 1987, and furnish a summary of experimental data from all working detectors on that day. The consistency of the experimental data from various detectors and the agreement with theoretical predictions are analyzed. The authors discuss whether the events registered by underground detectors on February 23, 1987, can be explained by neutrino radiation from the 1987A supernova.