Geographical pole

As the pole is referred to in geography and astronomy the intersections of the axis of rotation of a celestial body with the surface thereof.

Poles of the Earth

On earth, there are, consequently, the intersection points of the Earth's axis with the Earth's surface. For determining positions on the earth's surface with the high, lying in the centimeter range accuracy that is demanded of geographical applications today partially, the geographic poles are not suitable because they are not fixed but change due to the polar motion in the range of a few meters per year. This movement is not to be confused with precession and nutation. These are changing the direction of the rotation axis of the Earth. In the polar motion, the axis of rotation changes with respect to the earth body. For highly accurate position fixes today Cartesian coordinates a system is used, which is realized in the International Terrestrial Reference Frame ( ITRF ). It is essentially a system with high accuracy surveyed points of the earth's surface, which helps slow changes such as continental drift, mountain uplift, elastic tidal deformation and just Polbewegungen be compensated.

Poles of an ellipsoid of revolution

For this system of Cartesian coordinates can be an ellipsoid of revolution (eg the WGS84 ellipsoid) are correlated, which is then the basis for cartographic representations. The poles of this ellipsoid are different from the geographic poles. The north pole is placed in the direction of the positive z - axis of the Cartesian coordinate system. Generally, the direction of rotation of such a ellipsoid is referred to as prograde or prograde if, in the plan view of the pole, the rotation is counter clockwise, as the earth. Otherwise the rotation is called retrograde or retrograde.

Poles of celestial bodies

For the planets and moons of the solar system applies is a convention to the IAU 1970 that pole of a celestial body as the North Pole, which lies in the direction of the total angular momentum of the solar system. This corresponds roughly to the pole, the direction north of the ecliptic has (more precisely north of the Laplace plane of the solar system ). This means that in some celestial bodies - for example, Venus, Uranus and Pluto - according to IAU convention, the rotation is retrograde, that takes place at the North Pole in a clockwise direction.

This convention was not always taken into account, especially in bodies whose rotation axis considerable secular fluctuations such as asteroids and comets specifically. For these, often independent of the direction of the pole of rotation referred to counterclockwise as the north pole. Accordingly, the Working Group on Cartographic Coordinates and Rotational Elements ( WGCCRE ), the competent committee of the IAU, to produce a proposal for dwarf planets, asteroids and comets, the poles are determined by the that the rotation around the first principal axis of inertia is carried prograde. To avoid confusion, the poles are to be so designated, however, referred to as "positive" ( North ) or "negative " (south ) pole.

The right ascension of the north pole is indicated by and with the declination. As a starting point for the position of the prime meridian that ( with labeled) intersection of the equator of the celestial body is used with the celestial equator of the ICRF, which has the right ascension of 90 °. The angle between the intersection of the prime meridian and the equator of the celestial body and the point is specified.