Carmen Pérez González (Bergische Universität Wuppertal)
The average distance between adult eyes is about 7.5 cm, and objects as far away as 300 m can be viewed stereoscopically in pictures taken with a stereo camera whose two lenses are separated by this distance. However, in the case of the moon, the two pictures must be taken with two lenses some 100,000 kms apart. To solve this problem, already by mid 1850s the libration of the moon was being used to obtain the necessary baseline to produce lunar stereoscopic photographs. Even if the optical libration of the moon is a phenomenon that can be seen with the naked eye, its discovery was strictly tied to the development of telescopic observations of the Moon's surface in the first half of the seventeenth century. Libration results in 59% of the lunar surface being visible at one time or another. Towards the end of 1850s, the great amateur astronomer Warren de la Rue (1815-1889) used lunar photographs to produce extraordinary stereoscopic pictures by grouping pairs of photographs taken at different stages of lunar libration, as he explained in detail in his article "The Present State of Celestial Photography in England" (1859). In this paper, I will introduce the work of the most relevant pioneers in lunar stereoscopic photography (Warren de la Rue, Lewis Morris Rutherford and John Draper), and will explain the technical aspects involved in producing the images. The role of lunar stereographs (or more widely, astronomical stereographs) beyond the scientific arena will also be explored. In particular, I will analyze the presence of astronomical images in the "600 SET" of the Keystone View Company, and the contribution of the great astronomer E. E. Barnard (1857-1923) to these stereographs.