We report the first observations of an astronomical object using a superconducting tunnel junction (STJ) device, a pixel detector with intrinsic energy resolution in the optical wavelength range. The Crab pulsar was observed using a 6 times 6 array of Tantalum STJs at the 4.2-m William Herschel Telescope on La Palma. Each array element provides photon counting capability recording up to ~ 10^3 photons per pix per s with an arrival time accuracy of about 5 microsecond, and providing a wavelength resolution of about 100 nm. We derive a photometrically resolved light curve which, however, shows no significant colour index variations with pulsar phase.