(a square, to make equal), in Astronomy and Geography, a great circle of the sphere, equally distant from the two poles of the world, or having the same poles as the world. It is called equator because when the sun is in it the days and nights are equal; whence also it is denominated the equinoctial; and when drawn on maps, planispheres, or globes, it is called the equinoctial line, or simply the line. Every point in the equator is 90 degrees or a quadrant's distance from the poles of the world; and hence the equator divides the sphere into two equal hemispheres, in one of which is the northern, and in the other the southern pole. See Astronomy.