International Polar Motion Service

an international association of scientific institutions for the comprehensive study of the motion of the geographic poles. It was formed in 1961 in accordance with a resolution of the 11th General Assembly of the International Astronomical Union through the reorganization of the International Latitude Service, which had existed since 1898.

In addition to the periodic motions of the poles, a secular motion of the poles was observed in the mid-20th century in the direction of 76° W long, at a rate of 110 mm per year. It consequently became necessary to refer all latitude observations to some fixed origin. The International Polar Motion Service was given the responsibility of publishing the coordinates of the poles relative to the position of the mean pole at the epoch 1903.0; this point is called the international reference origin. In its calculations of the polar position the service also uses time and latitude observations made by observatories that are not members of the service. The central office at the service is located in the city of Mizusawa in Japan at the International Latitude Observatory.