Telescopes at the Papal Palace

Zeiss Visual Refractor Telescope

In the early 1930s, plans for a new Specola at Castel Gandolfo were prepared by the firm Carl Zeiss of Jena.

Construction began in 1932 and by 1935 it was mostly complete. The new visual refractor was installed under a large wooden dome 8.5 meters in diameter resting on the massive round construction of the palace’s ancient spiral staircase.

Zeiss provided a 40 cm objective of 6 m focal length, together with a set of 9 eyepieces and various accessories. The instrument was also provided with a Graff photometer for observing variable stars and with a micrometer for measuring double stars.

Later on a Danjon stellar interferometer was added. This was constructed in the Specola workshop and could be used for the determination of distances and positions of double stars and the diameters of planets.

  • Mounting: German mounting
  • Inauguration: 29 September 1935
  • Aperture: 40 cm
  • Focal Length: 600 cm
  • Image Scale: 34”/mm

 

Zeiss Double Astrograph

In the second rotating dome, 8 meters in diameter, also made of wood constructed on the solid foundation offered by the northeast corner of the palace, the principal instrument of the observatory was placed: the Zeiss Double Astrograph. 

It consisted of a refractor with a 40 cm four-lens objective of 240 cm focal length and a reflecting telescope with a 60 cm parabolic mirror of 200 cm Newtonian focal length and an equivalent 8.2 m focal length at Cassegrain focus. Both instruments plus two finders and a guide telescope were rigidly linked together and mounted on the same polar axis.

A large spectrograph could be mounted on the reflector for astrophysical research. The four-lens astrograph allowed 30×30 cm photographs with image correction to be taken; it was particularly suitable for photographic observations of variable stars and for the photographic determination of the positions of minor planets and comets.

  • Reflector:
    • Parabolic mirror,
    • Aperture 60 cm, Focal l. 240 cm
  • Mounting: German mounting
  • Inauguration: 29 September 1935
  • Refractor:
    • Four lens objective,
    • Aperture 40 cm
    • Chromatic correction 390 to 460 m
    • Focal l. 200 cm
    • Image scale 1.42’/mm
    • Field 8 degrees
  • Photographic plate 30×30 cm².
  • Newton System:
    • Plane secondary mirror,
    • 22 cm at 45
    • Image scale 1’.22/mm
    • Field 2.6o
  • Cassegrain System:
    • Convex secondary mirror
    • 15 cm
    • Equivalent focal l. 820 cm
    • Image scale 25"/mm
    • Field 50