In this map, the area outlined in red and labeled “頒暦所御用ヤシキ” (Hanrekishogoyouyashiki: Observatory for the Calendar; the lettering is upside-down from this angle) is the Astronomical Observatory in Asakusa constructed in 1782 (2nd year of the Tenmei Era). At first, this observatory was used to compile the Kansei Calendar. Afterwards, the Tenmonkata (Official Astronomer) continued to use it for observations until the fall of the Shogunate.

Previously, Torigoe Hill had been located in the northern part of the area shown in this map; and farther north was a pond named Himegaike. But to help ease the land shortage inside of Edo (now Tokyo), the pond was filled in and the hill was flattened. With the hill to the north gone and low lying river banks to the east and the south, this site had clear lines of sight, making it suitable for an observatory. Perhaps that’s why it was chosen.

In modern times when we think of observatories, we envision sites located far from urban areas to optimize the observing conditions. But looking at this map, to the north-west of the observatory is Torigoe Shrine; to the north is Jyusyo Temple; and to the north-east is Saifuku Temple, which is listed on maps of important Edo sites. Turning to the south where the Torigoe River is located, we find Fudasashi Gokaisei Kaisyo (a government accounting office). It can definitely be said that this is an urban area. On the other hand, since the observations don’t seem to have suffered due to being located within a city, we can get a sense of how dark the Edo nights must have been. The Astronomical Observatory in Asakusa is also included in Hokusai Katsushika’s “One Hundred Views of Mount Fuji” under the name Torigoe-no-fuji (Torigoe’s Unparalleled [View of Mt. Fuji]).

The Astronomical Observatory in Asakusa was demolished after the Meiji Restoration. Now, a display board marking the former site of the observatory has been installed at the Kuramae 1 Choume intersection (3-20 Asakusabashi Taito, Tokyo).

(Translator's Note: In addition to the standard Gregorian Calendar, Japan continues to use a reign era calendar. The different eras are defined by changes in the Japanese government, and accompanied by changes in Japanese society.)