National Astronomical Observatory of Japan

20-cm Telescope Dome

The Oldest Observation Building in Mitaka Campus

20-cm Telescope Dome

The 20-cm (7.9-inch) Telescope Dome was designed by the Construction and Repair Department of Tokyo Imperial University, and constructed by Mr. Chodayu Nishiura in 1921. This two-story building is made of reinforced concrete. The 20-cm Refractor Telescope, housed in the dome, was manufactured by the German company Carl Zeiss. Its equatorial mount has a weight-driven clockwork mechanism controlled by a governor. This telescope played a major role in sketching observations of sunspots for 61 years starting from 1938.

The 20-cm Telescope Dome is the oldest among the observation buildings in Mitaka Campus, but its design embodies functionality.

This building was listed as a Registered Tangible Cultural Property of Japan in February 2002.

Solar Observation Parties

Solar observation parties are regularly held at the 20-cm Telescope Dome. When conditions are right, participants can observe sunspots on the solar surface with the 20-cm Refractor Telescope operated by the staff.

Dates
To prevent the spread of the novel coronavirus, solar observation parties continue to be canceled until further notice.
Times
Only on sunny days from 10:00 a.m. to 2:30 p.m. or from 10:00 a.m. to Noon (in July, August, and September). In the summer season, the events may be canceled due to intense heat. After the observation parties, visitors can only view the telescope (until 5:00 p.m.).
How to Join
No fees or reservations are required. Our staff will be waiting at the telescope dome, so feel free to ask and join the party.

About

20-cm Refractor Telescope
Aperture20 cm (7.9 in)
Focal Length359 cm (11.8 ft)
MountWeight-driven clockwork drive
PurposeSunspot observations
Dome
SizeDiameter: 6 m (19.7 ft), Height: 7.8 m (25.6 ft)
StatusRegistered Tangible Cultural Property
Brief history
1921
(Taisho Year 10)
Completed
1927
(Showa Year 2)
Zeiss-made equatorial telescope installed
1998
(Heisei Year 10)
Retired from operation
2000
(Heisei Year 12)
Opened to the public
February 2002
(Heisei Year 14)
Listed as a Registered Tangible Cultural Property