Old Tokyo Observatories Used to Study Stars, Navigation

By Susumu Saito / Yomiuri Shimbun Staff Writer

12:40 JST, May 24, 2023

Down the street from Etchujima Station on the JR Keiyo Line, an old, small domed building surrounded by trees is an unusual sight in Koto Ward, Tokyo.

The building is actually one of two observatories of former Celestial Observatories of the Tokyo University of Mercantile Marine, currently known as Tokyo University of Marine Science and Technology, where students were trained to navigate ships.

The observatories were built in 1903 and were used from the Meiji era (1868-1912) to around between 1935 and 1944 to research astronomical ephemeris for navigation and astronomy.

Before World War II, the two-story First Observatory was equipped with an equatorial telescope that could track astronomical bodies according to their diurnal motion. The roof was also designed to rotate 360 degrees.

I received special permission to enter the building, and the first thing I noticed was how steep the stairs were. Soft light came in from the windows on the second floor, but the inside of the dome was dark, giving it a planetarium feel.

The one-story Second Observatory previously had a meridian instrument to observe the time when astronomical bodies pass through the meridian. It was also used to measure longitude, among other things.

The instruments in both buildings were removed by the U.S. military after the war and no longer exist.

“At the time, there were no means of communication, so knowledge of astronomy was essential for navigating the seas, where only the stars could be seen,” said Kuniaki Shoji, 75, a professor emeritus at Tokyo University of Marine Science and Technology.

The buildings were used for classes until the early Showa era (1926-89). After, it was used by a students’ association. Inside, there was an old photo of students looking through a telescope.

“I imagine they must have enjoyed themselves looking at the stars with other students, in addition to learning about the technology,” Shoji said.

The two observatories, which were not heavily damaged during the Great Kanto Earthquake or the Great Tokyo Air Raid, have been around for about 120 years. However, the area has now been built up and many tall buildings have made it difficult to observe the stars from the small structures.

As I looked back at the dome, I could picture students gathered around the telescope and tracing the path of the stars.

Former Celestial Observatories of the Tokyo University of Mercantile Marine

Address: Tokyo University of Marine Science and Technology, 2-1-6 Etchujima, Koto Ward, Tokyo

Access: About a 2-minute walk from Etchujima Station on the JR Keiyo Line

Memo: When the university festival “Kaiosai” is held on June 3 and 4, visitors can tour the sailing ship Meiji Maru, which is an important cultural asset of Japan.