she reaches the seventh, when her distance from
the sun at his setting is about one half the extent of the firmament,
one half of her is luminous: that is, the half which faces toward the
sun is lighted up by him.

4. On the fourteenth day, being diametrically across the whole extent of
the firmament from the sun, she is at her full and rises when the sun is
setting. For, as she takes her place over against him and distant the
whole extent of the firmament, she thus receives the light from the sun
throughout her entire orb. On the seventeenth day, at sunrise, she is
inclining to the west. On the twenty-second day, after sunrise, the moon
is about mid-heaven; hence, the side exposed to the sun is bright and
the rest dark. Continuing thus her daily course, she passes under the
rays of the sun on about the twenty-eighth day, and so completes the
account of the month.

I will next explain how the sun, passing through a different sign each
month, causes the days and hours to increase and diminish in length.

CHAPTER III

THE COURSE OF THE SUN THROUGH THE TWELVE SIGNS

1. The sun, after entering the sign Aries and passing through one eighth
of it, determines the vernal equinox. On reaching the tail of Taurus and
the constellation of the Pleiades, from which the front half of Taurus
projects, he advances into a space greater than half the firmament,
moving toward the north. From Taurus he enters Gemini at the time of the
rising of the Pleiades, and, getting higher above the earth, he
increases the length of the days. Next, coming from Gemini into Cancer,
which occupies the shortest space in heaven, and after traversing one
eighth of it, he determines the summer solstice. Continuing on, he
reaches the head and breast of Leo, portions which are reckoned as
belonging to Cancer.

2. After leaving the breast of Leo and the boundaries of Cancer, the
sun, traversing the rest of Leo, makes the days shorter, diminishing the
size of his circuit, and returning to the same course that he had in
Gemini. Next, crossing from Leo into Virgo, and advancing as far as the
bosom of her garment, he still further shortens his circuit, making his
course equal to what it was in Taurus. Advancing from Virgo by way of
the bosom of her garment, which forms the first part of Libra, he
determines the autumn equinox at the end of one eighth of Libra. Here
his course is equal to what his circuit was in the sign Aries.

3. When the sun has en