Etymologiae, Book III, chapters 59-66: De eclipsi lunae to De circulari numero stellarum
Chapter LIX. On the eclipse of the moon An eclipse of the moon occurs whenever the moon runs into the shadow of the earth. For it is thought not to have a light of its own but to be illumined by the sun, and hence it also suffers a failing if the shadow of the earth comes between it and the sun. And the moon suffers this on its fifteenth day, until such time as it passes out of the center and shadow of the obstructing earth and sees the sun, or is seen by the sun.
Chapter LX. On the difference between stellae, sidera and astra Stellae, sidera and astra differ from one another. For a stella is any single star. Sidera are formed of very many stars, such as the Hyades and the Pleiades. Astra are great stars, such as Orion and Bootes. But writers confuse these names, and use astra for stellae and stellae for sidera.
Chapter LXI. On the light of the stars The stars are said not to have a light of their own but to be illumined by the sun, as the moon is
Chapter LXII. On the position of the stars The fixed stars are immovable and are borne with heaven in perpetual motion, and they do not fall during the day but are obscured by the splendor of the sun.
Chapter LXIII. On the course of the stars The heavenly bodies are either carried or moved. Those are carried which are fixed in heaven and revolve with heaven. Some, like the planets, that is, the wanderers, are moved, and these accomplish their wandering courses within a fixed limit nevertheless.
Chapter LXIV. On the varied course of the stars Because the stars are carried through the different orbits of the heavenly planets, some that rose more quickly set later; some that rose more slowly come sooner to their setting; others rise together and do not set together; but all return in their own time to their proper course.
Chapter LXV. On the distances of the stars The stars are at different distances from one another and from the earth, and for this reason they appear to our eyes with unequal brightness, more or less. For many are greater than those we see conspicuous, but being placed farther off they seem small to us.
Chapter LXVI. On the circular number of the stars The circular number of the stars is that by which it is said to be known in how much time each star runs through its circle, whether in length or in breadth. For the Moon is said to complete its circle in a number of years, Mercury in 20 years, Lucifer in 9 years, the Sun in 19 years, Vesper in 15 years, Phaethon in 12 years, Saturn in 30 years. When these are completed, they return to the return of their circle, to the same places and parts. Certain stars, hindered by the rays of the sun, become irregular, or retrograde, or stationary, according to what the poet also remembers, saying:
The sun divides the seasons of the age: it changes day for night, and with its powerful rays forbids the stars to go, and by reason holds back their wandering courses.