EQUATOR

that great circle of our globe every point of which is 90° from the poles. All places which are on it have invariably equal days and nights. Our earth is divided by it into the northern and southern hemispheres. From this circle is reckoned the latitude of places both north and south.: There is also a _ corresponding celestial equator in the plane of the terrestrial, an imaginary great circle in the heavens the plane of which is perpendicular to the axis of the earth. It is everywhere 90° distant from the celestial poles, which coincide with the extremities of the earth’s axis, supposed to be produced to meet the heavens. During his apparent yearly course the sun is twice in the eelestial, that is, vertically over the terrestrial equator, on 2ist March and 23rd September. Then the day and night are equal all over the earth, whence the name equinox. The magnetic equator is a line at every point of which the vertical component of the earth’s magnetic force is zero; that is to say, a dipping needle carried along the magnetic equator remains horizontal. It is hence also called the aclinic line. It has a slightly devious course, but upon the whole keeps fairly near the geographical equator.