January 27: Issac Roberts

Isaac Roberts

January 27, 1829-July 17, 1904

Isaac Roberts was a Welsh astronomer who was a pioneer in photography of nebulae. He was a member of the Liverpool Astronomical Society in England and was a fellow of the Royal Geological Society. Roberts was also awarded the Gold Medal of the Royal Astronomical Society in 1895.

In 1883, Roberts began experimenting with stellar photography and by 1885 he had built an observatory with a 20-inch reflector. This allowed him to make significant progress in the then-developing field of astronomical photography.

Some deep space objects were too faint to be viewed by a normal telescope. However, these could be revealed using a photographic plate if the exposure was long enough. However, because the Earth rotates, the longer the exposure time was, the blurrier the image would be. On the other hand, if the exposure time was too short, then an image could not be produced due to the faint nature of these deep space objects. Isaac Roberts's solution to this dilemma was to develop a telescope/camera combination that would track the subject, allowing for a long exposure time as well as a clear image.

Some of his notable works include photographs of the Orion Nebula and Pleiades. Most consider Roberts's magnum opus to be a photograph showing the spiral structure of the Great Nebula in Andromeda, taken on December 29, 1888. His long exposure of the Andromeda Nebula revealed that it was actually a spiral nebula, which was quite unexpected at the time. Photographs such as this changed astronomy by revealing the true form of nebulae and clusters.

In addition to his considerable advancements in the field of astro-photography, Roberts also invented a machine called the Stellar Pantograver that could engrave stellar positions on copper plates.