With the invention of photography, whose first method of large diffusion was realized by the French Louis-Jaques Mandé Daguerre (1787-1851) and presented in Paris by the astronomer François Arago (1786-1853) in 1839, the ancient human dream of reproducing the real world, automatically and faithfully, on a bi-dimensional surface achieved its completion.
In parallel a new form of representation of the world , that allowed to reproduce it on a bi-dimensional surface also in its volumetric aspect, saw the light and developed itself. It was the stereoscopy, that is to say the tri-dimensional photography, a technique based on the principle of the binocularity of the human sight, according to which we can see the reality in its volumetric feature through the cerebral synthesis of the two different images perceived by each eye.
Photography was immediately applied also to astronomical subjects, at first to the most luminous stars, as the Sun and the Moon, and later to those fainter, as the comets. Gradually this happened also to stereoscopic photography.
The first comet to be photographed, still with modest results, was that of Donati in 1858. Of a better quality were the photographs of the big comets in 1881 and 1882, but to have results comparable to those of today we shall wait for the very good images of comet Morehouse in 1908, taken by the astronomer Edward Emerson Barnard (1857-1923).
With the arrival of the XX century photography superseded definitely the engraving and pictorial techniques in the scientific representation of comets, confirming what was predicted by the astronomer Georges Rayet (1839-1906) in 1887: The photography of big comets, of their nucleus and of part of their tail, is now an easy thing and no one of these stars will appear at the horizon without that a multitude of observers would not take them some photos.
In the picture: partial view of the exhibition in Oratory of St. Michael in Padua.
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