The sky charts
| The Carte du Ciel enterprise | ||
| A brief historical account | The Astrographic Catalogue | The sky charts |
In order to produce the sky charts, the photographic plates for the Carte du Ciel had to be transformed into engraved copper plates – a process which required a high degree of precision and was quite expensive – and then be printed on thick paper. Alternatively, the plates could be reproduced directly on photographic paper.
However, not all the zones of the sky could be photographed for chart-making, or even if the plates had been exposed, charts were not printed.
At the IAU 14th General Assembly, held in Brighton, UK, in 1970, the President of Commission 23 in charge of the enterprise, Paul Coderc (Paris Observatory) declared the Carte du Ciel an “unachieved project” and presented the following table which described its current status
| Sky zone | assigned to | carried out by | Sky charts |
| +90° to +65° | Greenwich | All charts printed | |
| +64° to +55° | Vatican | Heliogravures for 1/3 of +55°, +56°, +57°; the remaining printed on photographic paper | |
| +54° to +47° | Catania | NONE | |
| +46° to +40° | Helsingfors | NONE | |
| +39° to +32° | Potsdam | Uccle | Heliogravures for the entire zone printed and distributed by Uccle |
| +31° to +25° | Oxford | NONE | |
| +24° to +18° | Paris |
Heliogravures for the even zones +18°, +20°, + 22°, +24° | |
| +17° to +11° | Bordeaux | Heliogravures for the even zones +12°, +14°, +16° | |
| +11° to +05° | Toulouse | Heliogravures for the odd zones +5°, +7°, +9° | |
| +04° to -02° | Algiers | Heliogravures for the odd zones -1°,+1°,+3° | |
| -03° to -09° | San Fernando | Heliogravures for the odd zones -5°, -7°,-9° | |
| -10° to -16° | Tacubaya | Heliogravures for the zones -11°, -13 °, -15°, -16 ° | |
| -17° to -23° | Santiago | Hyderabad | NONE |
| -24° to -32° | La Plata | Cordoba | Heliogravures for the zone -25° only |
| -33° to -40° | Rio de Janeiro | Perth | NONE |
| -41° to -51° | Cape of Good Hope | NONE | |
| -52° to -64° | Sydney | NONE | |
| -65° to -90° | Melbourne | NONE |
On the whole, the information given in the table seems to match the lists of printed charts held at the Palermo Library, with some exceptions:
– Heliogravures by Uccle seem to cover only the zones +33°, +35°, +37°, +39°
– Some heliogravures for the zone +61°( Vatican) do exist
– Heliogravures for the zone +11° derive from plates taken at Algiers and not Bordeaux.
The image on the right evidences the information which identifies each sheet:
– Declination (e.g. Zone -1°)
– Chart number (N° 179)
– Observatory which issued the chart (Observatoire d’Alger)
– Date when the plate was taken (27 Octobre 1911)
– Name of the observer who exposed the plate (Mr. Renaux)
– Name of the printer (L. Schutzenberger)
Charts for each declination (e.g. +1°, +2° etc.) were taken at increasing right ascensions, and numbered accordingly. The varying lenght of the interval determined the total number of plates for each declination. E.g.: For intervals of 8 minutes, charts are 180 (from n. 1, derived from a plate having centre at 0h 4m AR (or 0h 0m), to n. 180, from a plate centered 23h 56m AR); for intervals of 12 minutes, charts are 120. For intervals of 10 minutes, charts are 144.
Links to sky zones in the table, lead to information on the work made at some of the Observatories involved with Carte du Ciel and to the lists of charts held at the Palermo Observatory Library.