The Zodiac, i.e., the Sphere of the Signs172, is the second sphere after the very great sphere, and is nearer the earth than the latter, and the Zodiac is also without stars, as I mentioned that the very great sphere was, and it moves from the east to the west of the world like the latter. The ancients imagined that there are nine spheres in all, and that it the Zodiac is one of the orbits of the very great sphere. Ptolemy refutes this theory in his own book, and says that he found a great difference between the very great sphere and the Zodiac as regards its zones and poles, for he found the north pole in the Zodiac twenty-four degrees higher than the same pole in the very great sphere, and he found the south pole of the Zodiac another twenty-four degrees under the same pole in the great sphere173. And the zones of this sphere are twenty-four degrees from each other in the top of the firmament174. Therefore Ptolemy establishes ten spheres, and we refer to the ninth sphere when we say that the sun, or moon, or other planet is in a certain degree in the signs of that sphere.
The reason that these names; Aries, Taurus, Leo, etc., are applied to the signs of the Zodiac is because the constellations in the sphere of the stars opposite that portion of the Zodiac which is called Aries or Taurus correspond in shape and nature to the same animals we have here below; but there is no figure at all in the Zodiac, because as I have stated, there is no star in it.
The philosophers divided the Zodiac into twelve parts, and called each part a sign, according to the name or shape of the thing which is beneath that sign in the straight line in the sphere of the stars. Similarly, they divided the year into twelve parts according to those twelve signs of the sun, and called the course of the sun in each of the signs a "month".
And the philosophers taught that the change of season occurs according to the course of the sun from sign to sign, and according to elevation or depression, for when the sun enters the first point of Aries175 an equinox occurs, i.e., equality of day and night, and then spring begins and does not depart until the sun is in the last point of Gemini; and when the sun enters Cancer, that is the beginning of summer. When it is there at the highest point of its sphere above, the sun heats the surface of the earth to a great extent, and when it arrives at
p.188the last point of Virgo, it brings the summer to an end. When it arrives at the last point of Libra, the second equinox occurs, and then autumn begins and does not depart until the sun is at the last point of Sagitarius. When it is in the last point of Capricorn, winter begins and continues until it is in the last point of Aries again, and then the spring begins again.
The reason that one winter is colder than another, and a winter wetter than another, and a winter drier than another and one summer hotter, and another drier than another, is because the sun is the cause of spring, summer, autumn and winter, and the other planets cause the same seasons176.
When the summer of the sun occurs, and the other planets are in the sign of their own winter, there is a great deal of rain and cold in the summer; and when the winter of the sun occurs, and the other planets are in the signs which show their own summer, there is wind and little rain and cold in that winter especially. And similarly as regards the other seasons. The heat and cold, dryness and wetness of the four seasons of the year depend upon the movements of the planets in the signs of the Zodiac, as the Blessed Creator himself has ordained them177.