The Sphere of the World

The Sun certainly always stays exactly on the ecliptic the apparent path of the Sun across the sky, but all other planets deviate either toward the north or toward the south; however, they are sometimes directly under the ecliptic. That part of the zodiac which deviates from the equinoctial the celestial equator toward the north is called "northern," "boreal," or "arctic." Those six signs from the beginning of Aries to the end of Virgo are called the northern signs. The other part of the zodiac which deviates from the equinoctial toward the south is called "meridional," "southern," or "antarctic." The six signs from the beginning of Libra to the end of Pisces are called the meridional or southern signs. When it is said that the Sun is "in Aries" or in another sign, it should be understood that this preposition "in" is used to mean "under," according to how we currently define a sign.

In another sense, a sign is defined as a four-sided pyramid whose base is that surface we call a sign, and whose vertex the pointed tip or peak is at the center of the Earth. According to this definition, properly speaking, we can say the planets are "in" the signs Because they are physically located within the volume of that pyramid.

In a third way, a sign is understood by imagining six circles passing through the poles of the zodiac and through the starting points of the twelve signs. These six circles divide the entire surface of the sphere into twelve parts that are wide in the middle but narrower near the poles of the zodiac; each such part is called a sign and takes its specific name from the sign captured between its two boundary lines. According to this definition, even the stars located near the poles are said to be "in" the signs.

Furthermore, imagine a solid body whose base is a sign (according to the definition just given), but whose sharp edge lies along the axis of the zodiac. In this fourth sense, such a body is called a sign; by this definition, the whole universe is divided into twelve equal parts called signs, and thus whatever exists in the world is located within one sign or another.

Concerning the Two Colures.

There are two other great circles circles that divide a sphere into two equal halves in the sphere which are called colures, whose function is to distinguish the solstices and equinoxes. The word "colure" comes from the Greek colon original: "colon", which means "limb" or "member," and uros original: "vros", which means "wild ox." This is because, just as the upright tail of a wild ox—which is one of its limbs—forms a semicircle and not a complete circle, so the colure always appears to us as imperfect or incomplete Medieval astronomers noted that because of the tilt of the sphere, these circles often appeared "cut off" or incomplete relative to the horizon.