Print on paper of a two times enlarged copper engraving image of the "Carte du Ciel" (zone of Uccle)
(Inv CDC N°39)
In order to fulfil the criterion of quality, every copper engraving had to be checked for mistakes before starting the final reproduction. Two distinct proofs were made in order to compare every glass plate with the copper engraving:
- a first print of the twice enlarged glass plate was obtained on photographic paper,
- a second print was made using the copper engraving itself.
In each case, black dots may represent the celestial objects. On a closer look, one can distinguish the figure of a triangle caused by the triple exposure. These three recordings were shifted with respect to one another by a small angle of size 5 or 6 arcseconds on the sky. A check of the proofs of each plate was next done to determine if the dots corresponded to a real object on the sky. Corrections to the copper engravings were also possible, if needed. Finally, in order to improve the precision further, the average of the three positions was computed for every star in the catalogue.
More information on the astrographic equatorial telescope which has contributed since 1908 to the mapping of the Uccle zone for the "Carte du Ciel" project and on the project see http://www.astro.oma.be/en/scientific-research/astronomy-astrophysics/carte-du-ciel/
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