Neutrino and gravitational wave astronomy: grand visions

Making an effort with the naked eye to observe the night sky means actually to make observations in a rather small wavelength interval from 300nm to 800nm and, hence temperaturewise in terms of black‐body radiation to deal with temperatures of 3000K to 10000K. How the sky would look if our eyes would be sensitive to neutrino radiation or gravitational waves, respectively? First of all, one would surely encounter the same problem as one encounters in the electromagnetic spectrum: One would be able only to observe some spectral lines in the very broad neutrino spectrum or spectrum of gravitational waves. However, the physics involved in those observations and their interpretation would be completely different, compared to the phenomena one is dealing with in the electromagnetic spectrum. Three astronomies seem to exist simultaneously in the future to expand the horizon of astronomical observation: Photon astronomy, neutrino astronomy, and gravitational wave astronomy. Sources of the radiation, their spectra, and ground‐based and space‐based observations for photons, neutrinos, and gravitational waves will be briefly reviewed.