The Sphere of the World (De Sphaera)

These are manifest, such as the equinoctial circle, the ecliptic, and the two circles parallel to the ecliptic, each having six degrees so that the zodiacal zone may be had, in which we distinguish the twelve signs. Likewise, we shall mark the tropics and the arctic and antarctic circles, and the six colure circles passing through the twelve points of the zodiac and its poles. We shall describe the remaining circles parallel to the ecliptic very lightly, and similarly those that pass through the poles of the zodiac and through all the degrees of the zodiac, as will be discussed in the second chapter of this work, through which we are able to mark the longitudes and latitudes of the fixed stars. For when we have a verified table of stars, we will be able to situate the stars on the sphere itself in this manner: since if there is a star of longitude 50 degrees and latitude 44 degrees, where the colure of 50 degrees of longitude on the sphere itself intersects the northern parallel if the star’s latitude is northern, or the southern parallel if it is southern, we shall mark that star, which we distinguish by form, color, or size so that one may understand in what order it is and the rest in a similar manner. We shall adapt to this solid sphere a straight and oblique horizon, as well as the meridian and the axis ending in the body of the earth, just as in the preceding sphere which was composed of eight circles.

A woodcut depicts an armillary sphere, representing the "Sphere of the World." The sphere consists of several intersecting rings and is held upright by a hand emerging from a decorative floral sleeve at the bottom. Labels within the diagram include: at the top of the axis, "Pole of the world or arctic"; upper left ring, "arctic circle"; upper right point on the ecliptic, "pole of the zodiac"; upper parallel ring, "tropic of Cancer"; the wide diagonal band, "zodiac" (decorated with astrological symbols for the signs of the zodiac, including Gemini, Taurus, Aries, Pisces, Aquarius, Capricorn); central horizontal ring, "Equinoctial"; lower parallel ring, "tropic of Capricorn"; lower left ring, "antarctic circle"; bottom of the axis, "pole of the world antarctic"; and a winding banner wrapped around the base of the axis, "Sphere of the World."