National Astronomical Observatory of Japan



Observatory History Museum

65-cm Telescope Dome

Observatory History Museum (65-cm Telescope Dome)

The 65-cm Telescope Dome (Observatory History Museum) was designed by Facility Department of Tokyo Imperial University and constructed by Mr. Yoshihei Nakamura in 1926. The construction of it is two-storied building made with reinforced concrete. The dome part is very rare because it was constructed with supporting of shipbuilders.

The observation floor (the red-brown floor of inside the second floor) moved up and down like an elevator. So, by raising or lowering the floor, an observer could look through the telescope comfortably even if the telescope was any direction.

The 65-cm Refractor Telescope was made by Carl Zeiss in Germany and boasts the largest aperture among refractor telescopes in Japan. After completion in 1929, it was used for a variety of observations as the largest aperture telescope until the 188-cm Reflector Telescope in Okayama Astrophysical Observatory was built in 1960. It was mainly used for determining the positions of stars that is the strong point for a long-focus (the tube is long) telescope.

It has retired from the observational research in March 1998, and now it has been kept quietly as a memorial of Japan astronomy. However, it is not broken any part, so it can be still used for observation.

It is not used for observation with getting older, but it is opened as Observatory History Museum with exhibiting panels for introducing history of the NAOJ in spring 2001. It is possible to learn about the history of astronomy and astronomical observation. Also, the copies of importance documents that NAOJ has are shown (the contents are changed twice a year).

This building has been registered a tangible cultural property of Japan in February, 2002.


65-cm Refractor Telescope
Aperture65 cm
Focal length1021 cm
Target of observationVarious astronomical photographic observation, spectroscopic observation
SizeDiameter 14.5 m, Height 19.5 m
RemarksRegistered Tangible Cultural Property (Structures)
Brief history
(Taisho era 15)
(Showa era 4)
Installation 65-cm equatorial
(Heisei era 10)
Research observation end
(Heisei era 13)
Open to the public as Observatory History Museum
February, 2002
(Heisei era 14)
Registered as Tangible Cultural Property of Japan