The Repsold Transit Instrument, designated as an Important Cultural Property, and its building, which is a Registered Tangible Cultural Property, were recognized in the 6th (FY 2023) Japan Astronomical Heritage list as “The Repsold Transit Instrument and the Repsold Transit Instrument Building.”

The Repsold Transit Instrument, with an effective aperture of 135 mm and a focal length of 2120 mm, was a professional-quality observation device at the dawn of modern astronomy. It was manufactured in 1880, by A. Repsold & Söhne in Germany. It was purchased by the Navy Meteorological Observatory under the Ministry of the Navy and placed in Iikura, Azabu (present-day Azabudai, Minato-ku, Tokyo). In 1888, when the Astronomical Phenomenon Observatory of the University of Tokyo, the Navy Meteorological Observatory, and the Geographical Bureau of the Home Ministry were merged to form the Tokyo Astronomical Observatory (TAO) of the University of Tokyo, the instrument was transferred to TAO and continued to observe from the same location. In 1924, when TAO (the precursor of present-day NAOJ) moved to Mitaka-mura, Kitatama-gun (now Mitaka City, Tokyo), the Repsold Transit Instrument was also relocated to Mitaka, and was later installed in the Repsold Transit Instrument Building completed in 1925, where it continued to be used for observations.

When the Repsold Transit Instrument was located in Azabu, it was used to determine the time of day as well as to make observations for measuring the local longitude. After being relocated to Mitaka, it was mainly used for observations of Solar System objects and astrometry observations, and remained active in the production of precise star position catalogs until 1963. The Repsold Transit Instrument was designated an Important Cultural Property in 2011, and the Repsold Transit Instrument Building was recognized as a Registered Tangible Cultural Property (structures) by the Japanese government in 2013. The Repsold Transit Instrument, a valuable instrument in the history of Japanese astronomy, is preserved in the Repsold Transit Instrument Building, which is maintained as the “Transit Instrument Museum,” and both can be seen in the Visitor’s Area of NAOJ Mitaka Campus, open daily to the public.

Japan Astronomical Heritage is recognized by the Astronomical Society of Japan for the purpose of carefully preserving historically valuable astronomy and calendar-related heritage, passing it on to future generations as a cultural heritage, and promoting awareness and utilization of them. This is the third time that something curated by the National Astronomical Observatory of Japan has been recognized as Japan Astronomical Heritage, following the 6-meter millimeter radio telescope at Mitaka Campus (in the second list in FY 2019) and the Temporary International Latitude Observatory’s Visual Zenith Telescope and related buildings in Mizusawa Campus (in the third list in FY 2020).