Introductory Astronomical Writings of the Ancients

is described by the foot of the Bear. The solstitial circle, moreover, is that which is held to be the most septentrional of all those that are described by the sun. When the sun has withdrawn itself into this circle, it completes its summer turning; and the longest day of the whole year, and the shortest night, result therefrom. After this turning, you may observe the sun by no means progressing further toward the north, but rather retreating toward the opposite parts of the world; hence, in Greek, it receives the name of tropic. The equator is that circle which is established as the largest of the equidistant circles: it is, indeed, so bisected by the horizon that one of its semicircles is placed above the earth, and the other is hidden beneath the earth. Upon this, the sun makes a twofold equinox, both vernal and autumnal. The brumal circle is that which, of all the circles that are described by the sun in the rotation of the world, pertains furthest to the south. Upon this, the sun makes its brumal turning; and the longest night of the whole year, and the shortest day, are produced. After this boundary, the sun by no means progresses further, but returns toward the other parts of the world; whence this one also is called tropical, as if it were a turning point. The antarctic circle, however, is equal and equidistant to the northern circle, and, touching the horizon at a single point, is furthermore entirely submerged beneath the earth; in it, the stars situated therein remain forever hidden from us. The largest of the five mentioned circles is the equator, then the tropics. The smallest, however (at least with respect to our habitation), are the arctic. Furthermore, these