Nobeyama radio observatory, Radio observatory in Minamimaki, Japan

Nobeyama Radio Observatory is a National Astronomical Observatory of Japan facility at 1,350 m near Minamimaki, Nagano. Its main instrument is a 45 m Cassegrain telescope with an aluminium-panel and CFRP-coated surface, built in 1981 and recognised as an IEEE Milestone in 2017. The site also holds the Nobeyama Millimetre Array of six 10 m dishes and the Nobeyama Radioheliograph, 84 antennas of 80 cm arranged along T-shaped baselines 490 m east-west and 220 m north-south.

Founded as an observing facility of the Tokyo Astronomical Observatory's radio astronomy division, the site held its groundbreaking ceremony in May 1969, and the Nobeyama Solar Radio Observatory opened that October. The 45-m millimetre-wave telescope was completed in 1981 and began shared use in 1982, the year the Nobeyama Radio Observatory held its opening ceremony. The solar observatory closed in March 2015, and the radioheliograph ended observations in March 2020.

Locals call the site "Nobeyama Radio Observatory," and its 45-meter dish was the first in Japan to offer shared observing time to universities nationwide. The Nobeyama Millimetre Array, six 10-meter dishes, was later moved to Osaka Prefecture and renamed SPART.

The site has a free car park and a guardhouse where group visits are registered and pamphlets handed out; the 45-m telescope has an observation building with a visitor room and monitor. In 2019 the dormitory-equipped main building closed and staff support was cut to weekday daytime hours, so check opening arrangements before travelling.

The telescope here contributed to detecting signs of intermediate-mass black holes near the galactic center. This observation helped astronomers understand the structure of the Milky Way better.