Former Temporary Latitude Observatory Main Building (Kimura

The Former Temporary Latitude Observatory Main Building: A Monument to Global Astronomy

Nestled within the grounds of the National Astronomical Observatory of Japan's Mizusawa VLBI Observatory in Oshu City, Iwate Prefecture, the Former Temporary Latitude Observatory Main Building stands as a quiet testament to one of Japan's greatest contributions to international science. Built in 1900, this modest yet elegant wooden structure served as the nerve center for a groundbreaking global collaboration in latitude observation — and became the very place where astronomer Kimura Hisashi made his world-famous discovery of the Z-term, forever changing our understanding of Earth's rotation.

Today the building is known as the Kimura Hisashi Memorial Hall, and it has been registered as a national Registered Tangible Cultural Property since October 2017. In 2024, it was further honored as a Japan Astronomical Heritage site by the Astronomical Society of Japan. Visitors can step inside this beautifully preserved Meiji-era structure and explore the instruments, personal effects, and archives that tell the story of how a small observatory in northern Japan helped unlock one of the mysteries of our planet.

Historical Background

In 1898, the International Geodetic Association resolved to establish a coordinated network of latitude observation stations around the world, all positioned along the 39°8' North latitude line. The goal was to precisely track the phenomenon of polar motion — the subtle wobble in Earth's axis of rotation that had been discovered in the 1880s. Six stations were established worldwide, and Japan's was placed in Mizusawa (now Oshu City), Iwate Prefecture.

The Temporary Latitude Observatory was officially founded in 1899, initially operating from a rented private residence. Construction of a permanent main building began immediately, and it was completed in March 1900. This building — the one that survives today — served as the observatory's administrative and research headquarters. It housed offices, research rooms, and served as the base of operations for the observatory's first director, Kimura Hisashi (1870–1943), a brilliant astronomer from Ishikawa Prefecture who had studied at Tokyo Imperial University.

Kimura meticulously analyzed the observation data from all six international stations. In 1902, he published a landmark paper revealing a previously unknown annual periodic variation in latitude measurements, which could not be explained by the known polar motion components alone. He introduced a new term — the Z-term — into the mathematical equation describing latitude variation. This discovery astonished the global scientific community and established Mizusawa as a center of astronomical excellence. Kimura received his doctorate in 1904 and was eventually awarded Japan's first-ever Order of Culture in 1937, along with the Gold Medal of the Royal Astronomical Society of Britain.

The building continued to serve as the main observatory building until 1921, when a larger two-story structure was constructed. It subsequently served as staff quarters and a records repository. During World War II, the Mizusawa observatory was the only latitude observation station in the world that continued observations without interruption.

Designation as a Registered Tangible Cultural Property

On October 27, 2017, the Former Temporary Latitude Observatory Main Building was officially registered as a national Registered Tangible Cultural Property (building). The designation recognizes the building as the original main hall of one of the six international latitude observation stations, and as a structure that conveys the history of the observatory to the present day.

The building is valued for several reasons. Architecturally, it represents a fine example of early Meiji-era Western-style institutional construction, designed by Kuru Masamichi of the Ministry of Education's architecture division. Historically, it is the oldest surviving building in the entire National Astronomical Observatory of Japan system. Scientifically, it is directly associated with the discovery of the Z-term, one of Japan's most important contributions to international astronomy. Additionally, three other structures on the observatory campus — the zenith telescope room, the zenith telescope target stand and its shelter — were registered as cultural properties at the same time, forming a comprehensive ensemble of early astronomical research facilities.

Architectural Highlights

The Former Temporary Latitude Observatory Main Building is a single-story wooden structure with a hip roof covered in san-kawara tiles (interlocking flat tiles). The building area measures approximately 164 square meters. The roof framing uses a king-post truss system, and the exterior walls feature weatherboard cladding (shitami-itabari), a characteristic of Western-style buildings in Meiji-era Japan.

The layout centers on a main entrance at the front, from which an L-shaped corridor provides access to four office rooms. The windows are Western-style sash windows that can be raised and lowered, adding an elegant touch to the facade. The overall design reflects the practical needs of a scientific institution while incorporating the Western architectural vocabulary that was standard for government buildings of the period.

Remarkably, this building has been moved three times during its existence. In 1967, when a new reinforced-concrete main building was constructed, the old structure was relocated northward by hikiya (building moving) on two occasions and rotated 180 degrees so that its entrance faces south. In 2007, it was moved approximately 10 meters further north onto a reinforced foundation for seismic strengthening. Despite these relocations, the building has been carefully maintained and retains its historical character.

Exhibits and Highlights for Visitors

As the Kimura Hisashi Memorial Hall, the building now houses a focused exhibition on the life and achievements of its most famous occupant. The director's office has been recreated with period furnishings to evoke the atmosphere of the early 1900s, complete with the very desk where Kimura is believed to have worked on his Z-term calculations.

Among the most significant exhibits is the Visual Zenith Telescope No. 1, the actual German-made instrument provided by the International Geodetic Association that was used for the observations leading to the Z-term discovery. Visitors can also see replicas of the Order of Culture — the first such decoration ever awarded in Japan — and the Royal Astronomical Society's Gold Medal, both presented to Kimura for his contributions. Historic abacuses, slide rules, and calculation tools used by Kimura are on display, as well as photographs and documents from the observatory's early decades. A recording of Kimura's own voice can also be heard in the exhibition.

The exhibition panels are designed to be accessible to visitors of all ages, including elementary school students, making this an excellent educational destination for families.

Literary Connection: Miyazawa Kenji

The Mizusawa Latitude Observatory also has a charming connection to one of Japan's most beloved authors, Miyazawa Kenji. In his early draft story "Kaze no Matasaburo" (written in 1922), which later evolved into the published work "Kaze no Matasaburo" (1934), the wind spirit character mentions passing through the Temporary Latitude Observatory in Mizusawa, noting it as one of the most important places in Japan because observations made there become known around the world. This literary connection adds another layer of cultural significance to the site, and it is believed that Miyazawa's visits to the observatory may have influenced his masterpiece "Night on the Galactic Railroad."

Visitor Information

The Kimura Hisashi Memorial Hall is located within the campus of the National Astronomical Observatory of Japan, Mizusawa VLBI Observatory. The memorial hall is free to visit. The adjacent Oshu Space Exploration Center (Oshu Uchu Yugakukan), housed in the former second-generation observatory main building (also a Registered Tangible Cultural Property from 1921), charges a separate admission fee.

The Oshu Space Exploration Center is open from 9:00 AM to 5:00 PM (last admission at 4:30 PM), and is closed on Tuesdays (or the following day if Tuesday falls on a holiday) and during the New Year holiday period. Admission to the Oshu Space Exploration Center is 300 yen for adults and students, and 150 yen for school children, with group discounts available.

To reach the site by public transportation, take the community bus from JR Mizusawa-Esashi Station (Tohoku Shinkansen) and alight at the Tenmondai-mae bus stop, which is about a one-minute walk from the memorial hall. The bus journey takes approximately 21 minutes. By car, the observatory is about 10 minutes from the Mizusawa Interchange on the Tohoku Expressway.

Surrounding Attractions

The Oshu City area offers a wealth of cultural and historical experiences that complement a visit to the Kimura Hisashi Memorial Hall. Visitors can explore the Oshu Space Exploration Center next door, which features interactive exhibits on astronomy, a 4D Digital Universe Theater developed by the National Astronomical Observatory, and displays on the region's connection to space science including the VLBI radio telescope array.

The Esashi Fujiwara Heritage Park, about 15 minutes by car from Mizusawa-Esashi Station, is Japan's only Heian-period historical theme park. It faithfully recreates over 120 buildings from the era of the Oshu Fujiwara clan and has served as a filming location for numerous NHK historical dramas. Visitors can try on period costumes and practice archery.

Hiraizumi, a UNESCO World Heritage Site, lies approximately 20 minutes south by car. The golden Konjikido hall of Chuson-ji Temple and the Pure Land garden of Motsu-ji Temple are among Japan's finest examples of Heian Buddhist art and architecture. The Komagatake Shrine in Mizusawa, with over 1,500 years of history, is known as a power spot for victory and good fortune.