Poles

Poles (Gr. polos, a 'turning-point'), in Geography, are the two extremities of the axis round which the earth revolves; they are therefore situated the one on the north, and the other on the south side of the equator, and equidistant from all parts of it, or in 90° N. lat. and 90° S. lat. They are called the north and south poles of the Earth (q.v.).—In Astronomy the poles, which, for distinction's sake, are frequently denominated 'celestial poles,' are those points in the heavens to which the earth's axis is directed, and round which the heavens seem to revolve. The celestial poles are valuable points of reference to astronomers and geographers, so that the determination of their position in the heavens is a matter of the utmost importance. Unfortunately, no stars mark their exact situation (see POLE-STAR)—though there is a minute telescopic star only a few seconds from the north pole, which may be employed instead of it in rough observations—and therefore it is necessary to adopt some means for discovering its precise position. This is effected in the following manner: A bright star (generally the pole-star) is selected, and its position in its upper and its lower Culminations (q.v.) is accurately noted; the point midway between these two positions of the star is the pole of the heavens. The observation of the star's two positions must be corrected for refraction, and it is for this reason that the pole-star is selected, since the effect of refraction is much the same in both positions of the star. The term 'poles' has, however, a wider application, as denoting the extremities of a line passing through the centre of a great circle perpendicular to its plane; thus, we have the poles of the horizon (viz. the zenith and nadir), the poles of the ecliptic, the poles of a meridian; and, in the same sense, the terrestrial and celestial poles are spoken of as the poles of the equator and equinoctial respectively.—Pole, in Physics, denotes those points of a body at which its attractive or repulsive energy is concentrated; see POLARITY, and MAGNETISM.