Complete Works, Volume Four

insofar as the sphere moves on its own poles, the whole thing is moved by a single snatching motion upon the poles of the World.

Indeed, even though the lower heavens perform special motions by which they seem to withdraw toward the East, following the circle soon to be called the Zodiac, they are all snatched toward the West by a single force from the "First Mover" original: "Primo mobili," the outermost sphere in Aristotelian cosmology that moves all others situated above. They are carried around within the same period of twenty-four hours. For this reason, the stars placed within them appear to rise and set, or to come and go, every day. This motion impressed upon them is called the Snatching Motion original: "motus Raptus".

Meanwhile, this Snatching implies that all the heavens must be not only transparent, but also touching, solid, and hard. It also implies that the stars are fixed in them so they can be snatched along together. Although this may not be true in reality, it can be admitted as a hypothesis for explaining the motions.

Regarding the circles of the sphere, they are distinguished as ten in number. Six of these are called Major or Great circles, because each of them divides the sphere into two equal parts. These are the Horizon and the Meridian, within which the others revolve. Additionally, there are the Equator, the two Colures, and the Zodiac, which is a wider circle. Along the middle of the Zodiac is drawn the line called the Ecliptic.

Four circles are called Minor, because each divides the sphere into two unequal parts. These are the two Tropics and the two Polar circles. Together with the Equator, these are called Parallels because they are equidistant from each other at all points.

I mentioned in passing that the Zodiac circle is wide. This implies that the other circles should be conceived as indivisible lines. Even if such lines are not found on a physical sphere because they cannot be made or joined that way, they must be conceived by the mind. I say "conceived" because when we look for them in the sky, they are perceived by the mind alone, with the exception of the Horizon.

There are other circles to be understood in the sky as well, but those will be discussed later.

It should be noted here that any circle is usually divided into 360 equal parts called degrees. Each degree is understood to be subdivided into 60 small parts, which they call First Minutes, or simply Minutes. In the same way, each first minute is understood to be subdivided into 60 parts called Seconds. Each second into 60 Thirds, and so on into Fourths, Fifths, and so forth, if needed.

Similarly, since the Day is divided into 24 hours, an hour is subdivided into 60 First Minutes. Each first minute into 60 seconds, and each second into 60 thirds.

CHAPTER II.

On the so-called Celestial Globe, insofar as it is the same as the Sphere.

The mentioned circles of the sphere are also commonly represented on that object handled by everyone, called the Celestial Globe. This globe is the same as the sphere, provided that the empty spaces between the moving circles of the sphere are understood to be filled in, rounded out, and marked with the images of the stars.

The surface of the globe represents the face of the Firmament, or the view of the Fixed Stars. These were long ago organized into certain figures or images called asterisms original: "ἀστερισμοὺς," meaning groups of stars, constellations, or celestial signs. Because Aratus described them following Eudoxus, some call the celestial globe the Aratean Sphere.

Furthermore, the constellations have been distinguished since ancient times into 48 groups. These include the stars visible in Greece and the entire known part of the world at that time. Twelve of these are described in the Zodiac. Twenty-one are to the North of the Zodiac, and fifteen are to its South. They are often expressed in these verses:

Twelve celestial signs are in the zodiac belt;
They are Aries, Taurus, Gemini, Cancer, Leo, Virgo,
Libra, Scorpio, Sagittarius, Capricorn, Aquarius, Pisces.
Toward the North, twenty-one are seen:
Ursa Minor, Major, Boötes, Draco, Corona Borealis, Hercules
the Kneeler, Lyra, Cygnus, Cepheus, and Cassiopeia,
Perseus, Andromeda, Triangulum, Auriga, Pegasus,
Equuleus, Delphinus, Sagitta, then Aquila, Ophiuchus, Serpens.
Finally, fifteen are noted turning toward the South:
Cetus, and Eridanus, Lepus, the star of Orion;
Sirius, and Procyon, the ship Argo, and Hydra, Crater,
Corvus, Centaurus, Lupus, Ara, and Corona Australis, Piscis.

In recent times, after stars invisible to the ancients were discovered by sailing south, eighteen more constellations were distinguished, besides two nebulas. Twelve of these have been organized into numbers, contained in this couplet:

Phoenix, Grus, Indus, Dorado, Pavo, Apus, Hydrus,
Tucana, Triangulum Australe, Musca, Chamaeleon.

I pass over certain smaller constellations designated within the larger ones, such as the Pleiades and Hyades in Taurus, the Manger and the Asses in Cancer, and the She-Goat and Kids in Auriga.

I also pass over some stars in the constellations themselves...