National Astronomical Observatory of Japan

Okayama 188-cm Reflector Telescope and its Dome

Night Scape Photograph・

Okayama 188-cm Reflector Telescope and its Dome

The 188-cm Reflector Telescope in Okayama Astrophysical Observatory is an optical infrared telescope manufactured by Grubb Parsons, UK. Because the effective diameter of the primary mirror is 74 inches (188 cm), it is called “Nana-yon (meaning seven-four in Japanese)”. It was completed in 1960.

The dome housing Nana-yon is huge: its diameter is 20 meters, its height is 23 meters, and its weight is 150 tons. The dome’s observation window is 6 meters wide by 22 meters long. By rotating the dome, this opening can be pointed in any direction.

A Telescope Born in the UK

The Okayama 188-cm Reflector Telescope was made by Grubb Parsons in the UK. Telescopes of the same aperture size manufactured by this company also exist in Canada, Australia, South Africa, and Egypt. Unfortunately, the 188-cm Reflector Telescope at Mount Stromlo Observatory in Australia was destroyed by a wildfire in 2003. The focal length of the 188-cm Reflector Telescope’s primary mirror is 915 cm. Its body tube has an elongated octagonal truss structure. Also, by exchanging the secondary mirror, you can switch between three different focal points: the Newtonian focus, Cassegrain focus, and Coude focus. Today, we observe mainly with instruments mounted at the Cassegrain focus, such as HIDES-Fiber (High Dispersion Echelle Spectrograph), ISLE (Near Infrared External Spectroscopy) and MuSCAT (Multi-color Simultaneous Camera for studying Atmospheres of Transiting exoplanets).

Text by: Hiroyuki Toda (Okayama Astrophysical Observatory)
Translation by: Hiroko Tsuzuki and Ramsey Lundock (Public Relations Center, NAOJ)

Image Data

DateFebruary 2017
PhotographerYutaka Iijima
CreditYutaka Iijima

Related Link