“Carte du Ciel” Telescope

Astronomers in Paris in 1887 set up the basis for the first photographically-based atlas of the stars: the Carte du Ciel (Map of the Sky). Based on photos, first a map and then a catalogue of the stars would be made. Eighteen observatories located in countries on all continents participated in the project. 

The Vatican Observatory was given its swath of the sky to map between the parallels of +55 and +64 deg. The Paris agreements provided that all of the eighteen observatories participating in the Carte du Ciel would obtain instruments that had the same characteristics so that a perfect homogeneity of the results would be assured. 

The characteristics of the objective gave, on a photographic plate 16 cm square, a useful field 13 cm square, equivalent to two degrees on the sky, about four times the diameter of the moon. The scale, therefore, was about 1 arc-minute/mm.

The photographic equatorial telescope and the rotating eight meter dome, constructed at Paris in the Gilon workshops, were set in place on the Leonine Tower in 1891, close to the present-day location of the Vatican heliport and known today as the Torre S. Giovanni (St. John’s Tower). It has walls a good four and a half meters thick and is one of the few bastions still standing of the fortification which was called “leonina” because Saint Leo IV had it built in 840 as a defense against the Saracen invasions. The telescope was moved to the summer gardens of Castel Gandolfo in 1942; the final plates for this project were taken in 1953.

• Mounting: English mounting
• Inauguration:
• Moved from The Vatican to Castel Gandolfo,
• was newly inaugurated in 1942.
• Refractor: Double refractor
• Astrograph:
• Aperture 33 cm
• Focal l. 343 cm
• Photograpic plate 13×13 cm²
• Image scale 1’/mm
• Field 2 degrees
• Collimator:
• Aperture 20 cm
• Focal l. 360 cm

Schmidt Telescope

In 1949 a Schmidt telescope was ordered from the firm of Hargreaves and Thomson of London. Five years later work began on the construction of the Schmidt building, joined to the dome built in 1942 for the Carte du Ciel. The telescope was delivered in 1957; after several years for installation and testing, observational programs began in 1962.

The instrument has a spherical mirror 98 cm in diameter, with a 65 cm corrector plate (its aperture) mounted at the center of curvature of the primary near the tube opening. The focal length is 2.4 meters. The 20 × 20 cm photographic plate is placed at the focal plane, about half way down the tube. The usable field is about 5 × 5 square degrees, more than six times larger than that of the Carte du Ciel astrograph. 

For spectroscopy it used a combination of three objective prisms at the tube opening; these prisms are among the most powerful in the world. The Schmidt telescope was used for about twenty years to study the evolution of star clusters by stellar spectroscopy and polarimetry; unfortunately, light pollution from the surrounding towns made the site unusable by the early 1980s.

• Mounting: Fork mounting by Thomson & John Bowton Ltd
• Optics: Optics by Hargreavers & Cox
• Inauguration: 16 November 1957
• Spherical Mirror:
• Apert. 98 cm
• Focal l. 240 cm
• Correcting lens, 65 cm
• Image scale 1’.26/mm
• Field 5 degrees square
• Photographic plate 20×20 cm²