National Astronomical Observatory of Japan

Discovery of Japan’s Oldest Photographic Plates of a Starfield

| Science

A team lead by Jun-ichi Watanabe and the Public Outreach and Archive Office has been inspecting as many as 20,000 old photographic plates, which were found in a pile of cardboard cartons. In the course of their inspections, the team has discovered 437 plates recorded from the end of the 19th century to the beginning of the 20th century. This was the first era in which observations were recorded using photographic plates in Japan.

Most of the plates were obtained by using the Brashear astrograph at Azabubu in the 19th century. The oldest photographic plate was marked (delete ‘as’) No.13 and was recorded on March 5, 1899. The team also found a number of historically important plates; among these are images of the first minor planet “TOKIO” that was detected in Japan and named after our country, and of a star 61 Cyg, with a large proper motion.

We have long known that Tokyo Observatory of Tokyo Imperial University began its observations at Azabu. However, for many years, everyone believed that all the plates and observational instruments were lost in the chaos following the Great Kanto earthquake (1923) and in a fire that damaged Tokyo Observatory’s main building, events that took place before and after the Observatory’s move to Mitaka.