Chapter 34: On the solstices and equinoxes

2. There are two solstices: first, the summer solstice, eight days before the Kalends of July, from which time the sun begins to return to the lower circles; the second, the winter solstice, eight days before the Kalends of January, when the sun begins to make for the higher circles, whence the day of the winter solstice is the shortest and that of the summer solstice the longest.

3. Likewise there are two equinoxes: one in the spring and the other in the autumn, which the Greeks call ἰσημερίαι. These equinoxes are the eighth day before the Kalends of April and the eighth day before the Kalends of October, because the year formerly was divided into two parts only, that is, into the summer and the winter solstice, and into two hemispheres.