Take a Journey through Japan's History of Astronomy in Tokyo

World's First Photo of a Black Hole "Shadow"

The National Astronomical Observatory of Japan (NAOJ) is comprised of 12 facilities in Japan, including the NAOJ Mizusawa in Oshu City, Iwate Prefecture, and the NAOJ Nobeyama Radio Observatory in the Minamisaku district of Nagano Prefecture. They also have six overseas facilities, including the Subaru Telescope in Hawaii and the ALMA operations support facility in Chile. The oldest of these facilities, and the one with the most history, is the Mitaka Campus, where the NAOJ is headquartered. The Tokyo Astronomical Observatory was established in 1888 in the Iigura area of the former Azabu City in Tokyo, before being moved to its current location in 1924. In 1988, the facility was reconstituted into the National Astronomical Observatory of Japan.

Public relations officer Koike Akio says, "The NAOJ is a research institute that plays a central role in the field of astronomy in Japan. Its mission is to conduct research at the very cutting-edge of human knowledge. As an inter-university research institution, we provide many researchers with access to our astronomical observation and research facilities, and have participated in many joint projects with overseas research institutions. In recent years, we played an important role building observation systems and conducting analyses for the Event Horizon Telescope (EHT) project, which succeeded for the first time ever in capturing an image of a black hole 'shadow.' Unlike when the observatory first moved into the area, Mitaka City has become quite urban and isn't a very suitable location for an observatory anymore. However, we hope that many people will visit the facility, as it's a great opportunity to learn about the process of Japanese modernization through the lens of astronomy."

The facility, which is open to visitors free of charge, sees many international tourists, and has leaflets available in five languages. Visitors can listen to an audio guide in English or Japanese (equipped with a sign language video) on their smartphones or tablets, etc., in order to gain more detailed information about the facility.

An Observatory Built about a Century Ago

The Mitaka Campus, which has an area of approximately 260,000 square meters, is lushly wooded, with visitors able to look around the old observatory while strolling through the abundance of greenery. The followings are some of its most well-known buildings.

The 20-cm Telescope Dome, built in 1921 and located close to the main entrance, is the oldest of the buildings still standing on the Mitaka Campus today. The building was used to observe sunspots on the Sun for 60 years, from 1938 to 1998.

"The telescope was made by the German company Carl Zeiss. It tracks the sun automatically through a weight-driven clockwork drive that utilizes weights. An image of the sunspot is projected onto a plate at the edge of the telescope. The position and shape of the sunspot is recorded by tracing it with a pencil. We currently host solar observation sessions, mostly on weekends," says Koike.

The Observatory History Museum (formerly the 65-cm Telescope Dome) was built in 1926, the telescope was installed in 1929. The wooden dome houses a massive refractor with a 65-centimeter aperture. It had been the largest aperture of any telescope in Japan at the time, and succeeded in various observations until 1998, including measuring the position of stars. Nowadays, the building has become a place to learn about the history of astronomy and astronomical observation, featuring exhibition panels describing the history of the NAOJ.

The Solar Tower Telescope, also known as the Einstein Tower, was completed in 1930. The telescope is designed to detect the slight changes in the solar spectrum caused by gravity. Sunlight streaming in through the rooftop dome is directed downward to the prism in the semi-basement, which splits it into a spectrum of colors. The building made valuable contributions not just to the field of astronomy but also physics, and has been designated as a Tangible Cultural Property.

Nowadays, the NAOJ's cutting-edge observational instruments are located in places with better observational conditions, both within Japan and overseas, and the Mitaka Campus serves as a base for research and the development of equipment. In the Mitaka Open House event, which is held every year, visitors can talk directly to researchers about state-of-the-art research. The facility is making active efforts to promote the beauty and appeal of astronomy on a broader scale—for instance, through the 4D2U (Four-Dimensional Digital Universe) Dome Theater events, held three times a month, which allow visitors to view observation data in the form of 3D images.

Wander the historical buildings of the Mitaka Campus of the NAOJ, and get a glimpse into the history of astronomy, and the mystery and intrigue of space. The hope is that more visitors—from Japan and also from overseas—visit this wonderful facility.