Japan 1949 – Mizusawa Latitude Observatory
The International Latitude Observatory at Mizusawa in northern Japan was founded
in 1899 as one of six stations of the International Latitude Service (ILS, the
forerunner of the modern International Earth Rotation Service), with Hisashi Kimura as its first director. The other ILS observing stations were: Tschardjui
(Russia), Carloforte (Italy), Gaithersburg (USA), Cincinnati (USA) and Ukiah
(USA), all chosen to be close to the same latitude, 39° 08’ north. By measuring precise star positions, these observatories tracked slight
changes in latitude caused by motion of the Earth’s axis of rotation (polar motion).
Mizusawa, Carloforte, Gaithersburg and Ukiah were initiallly equipped with a
108-mm (4.25-inch) Visual Zenith Telescope made in Germany. However, the
telescope shown on this stamp commemorating Mizusawa’s 50th anniversary is the 178-mm (7-inch) Floating Zenith Telescope, a
photographic instrument introduced at Mizusawa in 1939, made in Japan but with
Zeiss optics.
Mizusawa Latitude Observatory served as the Central Bureau of the ILS from 1922
to 1934 and again from 1962 to 1987 (when the ILS became the International
Polar Motion Service). It is now known as Mizusawa Astrogeodynamics
Observatory.
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