National Astronomical Observatory of Japan

Repsold Transit Instrument Building

Transit Instrument Building

The Observations by the Repsold transit instrument were done in this building that was built in 1925.

The Repsold transit instrument which is stored was made in Germany in 1880. When the Tokyo Astronomical Observatory was in Azabu, it had been used for the measurement of longitude and the determination of time. The point where the transit instrument had been has become one of the origin of astronomical longitude.

After the observatory was moved to the Mitaka campus, the transit instrument was placed at this building and it had been utilized for the observations of the right ascension of the Moon, planets, and asteroids. After 1937, it had been used mainly for the observations of the right ascension of the fixed stars. In 1949, the first full-fledged catalog “the Catalog of Mitaka Zodiacal Stars” was published. And in 1962, “the Catalog of Mitaka Equatorial Stars” was also published, but the observation by the Repsold transit instrument was finished at the same time of the end of equatorial stars observation.

The pillar top and entrance eaves of the housing were decorated with the secession style which was popular at that time.

Repsold Transit Instrument

Repsold Transit Instrument

The Repsold transit instrument was made by A. REPSOLD & SÖHNE, Germany, in 1880 (Meiji era 13). In 1881 (Meiji era 14), the Navy Meteorological Observatory of the Navy Ministry of the Meiji Government bought it with the price at the time, it's 15,200 Deutsche Mark. It was full scale astronomical instrument in the dawn of modern astronomy with 135-mm of effective aperture and a focal length of 2120 mm. At that time, the Navy Meteorological Observatory was in Azabu-iigura. When Tokyo Astronomical Observatory of University of Tokyo was inaugurated with integrating with Astronomical Phenomenon Observatory of University of Tokyo, Navy Meteorological Observatory, and the Geographical Bureau of Home Ministry in 1888 (Meiji era 21), the observatory was placed at the same location where was the Navy Meteorological Observatory. Then the control of the Repsold transit instrument was transferred to Tokyo Astronomical Observatory.

Transit instrument is used for determining the longitude of the place by observing time of passage on meridian of stars in precisely, and/or used in the observation to determine the time.It is the historical instrument because the midday gun fired at the time that was determined by the observation of this transit instrument on the site of the tower of Edo Castle. Still now, the area at the Azabu-iigura is little space, and also the sky had been become brighter and unsuitable for observation because the place was urban area.

Because of this, Tokyo Astronomical Observatory went ahead with the relocation plan to Mitaka of Kita-tama county where is able to have dark and large area. However, there was Japanese-Russo War during 1904 (Meiji era 37) to 1905 (Meiji era 38). Even after Japan won the War, the national condition of Japan was extremely exhausted by the huge war cost. So, getting the place for the relocation was in 1909 (Meiji era 42), and the fund-raising for the relocation expenses was not made the desired progress.

Tokyo Astronomical Observatory movement to the Mitaka was started from 1914 (Taisho era 3), but the work was late. In September 1, 1923 (Taisho era 12), Tokyo Astronomical Observatory in Azabu-iigura was suffered catastrophic damage by Great Kanto Earthquake. However, with the luckily, the Repsold transit instrument was able to escape from the damage. By taking this earthquake opportunity, the relocation to Mitaka of Tokyo Astronomical Observatory was proceeded at once. The Repsold transit instrument was also moved to the housing of Repsold transit instrument that was built in 1925 (Taisho era 14).

After moving to Mitaka, it was used for the determination of right ascension of the Moon, large planets, and mainly asteroid from 1935 (Showa era 10). And then it was used to determine the right ascension of stars by differential observation. From 1937 (Showa era 12) to 1943 (Showa era 18), the right ascension of zodiac stars (2790 stars) were determined and completed “Tokyo Mitaka Catalogue of Zodiac Stars” (1949) that is the first full-scale star catalog in Japan. Also, the right ascension of stars in equatorial (4135 stars) were determined by the observation from 1950 (Showa era 25) to 1959 (Showa era 34) and published “Tokyo Mitaka Catalogue of Equatorial Stars” (1962). The Repsold transit instrument completed the observations of stars in equatorial, and then finished its role.

The Repsold transit instrument is valuable telescope as the basic astronomical instrument with having more than 130 years histories in the history of Japanese astronomy.

The Repsold transit instrument has been designated as an important cultural property of Japan in June, 2011.


Repsold Transit Instrument
Aperture13.5 cm
Focal length212 cm
Target of observationaccurate positional observation of celestial objects
RemarksImportant cultural property of Japan
SizeHeight 5 m
RemarksRegistered Tangible Cultural Property (Structures)
Brief history
(Taisho era 14)
(Showa era 24)
Completed “Tokyo Mitaka Catalogue of Zodiac Stars”
(Showa era 25)
Published “Catalogue of Zenith Stars”
(Showa era 37)
Published “Catalogue of Mitaka Equatorial Stars”. and research observation end
(Heisei era 20)
Open to the public as Transit Instrument Building
June, 2011
(Heisei era 23)
Repsold Transit Instrument has been designated as an important cultural property of Japan
April, 2014
(Heisei era 26)
The housing of Repsold Transit Instrument has been registered as tangible cultural property of Japan