Andromeda Galaxy). He made the photo on 29 December 1888, using his 20-inch aperture reflecting telescope made by Grubb. The long exposure photograph revealed that the nebula had a spiral structure, which was quite unexpected at the time. Photographs such as this changed astronomy by revealing the true form of nebulae and clusters, and eventually helped to develop the theories about galaxies. He published his celestial portfolio in a large format book that is the first popular account of celestial photography of the deep sky. In addition to his considerable advancements in the field of astrophotography, Roberts also invented a machine called the Stellar Pantograver that could engrave stellar positions on copper plates. The Science Museum (London) has Robert's 20-inch reflector. See also Isaac Roberts' Observatory Notes References External links Isaac Roberts (1829–1904), biographical information by Bryn Jones 1829 births 1904 deaths People from Denbighshire Welsh astronomers Welsh agnostics Fellows of the Royal Society Fellows of the Royal Astronomical Society Recipients of the Gold Medal of the Royal Astronomical Society