Исаак Робертс: Астрофотографияның иондастырушысы

Welsh astronomer

Isaac Roberts FRS (27 January 1829 – 17 July 1904) was a Welsh engineer and businessman best known for his work as an amateur astronomer, pioneering the field of astrophotography 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 1878, Roberts had a 7 inch refractor at his home in Rock Ferry, Birkenhead. Although at the time he used this for visual observation, he began to explore stellar photography, his forte, a few years later. In 1883, Roberts began experimenting with astrophotography. He first used portrait lenses with apertures varying from ⅜ to 8 inches (9.5mm to 203mm). Roberts was pleased with the results, and ordered a reflecting telescope with a silver on glass mirror of 20 inch diameter (100 inch focal length) from the Grubb Telescope Company and by 1885 he had built an observatory building to house it. He mounted photographic plates directly at the prime focus to avoid the loss of light that would occur from using a second mirror. This allowed him to make significant progress in the then developing field of astrophotography. In 1886 Roberts displayed his first photographs at the Royal Astronomical Society at Liverpool, of which he was president. These images showed, for the first time, "the vast extensions of nebulosity in the Pleiades and Orion."

Astrophotography requires very long exposure times (sometimes an hour or more) to record faint objects on a photographic plate. Long exposure could also record objects invisible to the human eye. Isaac Roberts developed a technique of "piggyback" astronomical photography, mounting the camera/lens on a larger equatorial mounted telescope that was used as a "guidescope". The combination kept the camera aimed accurately over the long exposure time as the Earth rotated. Most consider Roberts' magnum opus to be a photograph showing the structure of M31, the Great Nebula in Andromeda (now known as the 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.