In 1987, astronomers found a nearby supernova. The stream of neutrinos it had emitted were detected all around Earth. Those neutrinos arrived at the Earth a few hours before light from the supernova did, apparently because the neutrinos weren’t slowed down through interactions with dust and other matter along the way. So neutrinos can provide a first alert for astronomers, suggesting where they should point their telescopes to catch major upcoming events.