...the variety of things, and various apparitions appear in the air; about which Lucan later sang in this manner:

"Nights beheld unknown and obscure stars, the pole burning with flames, and torches flying obliquely through the empty void of heaven; they saw the hair of a fearsome star—the comet that changes the kingdoms of the earth."

Although many more apparitions of this kind are sometimes observed. For it often happens that whatever catches fire in the upper reaches of the air attains an equal length and width; in such cases, this phenomenon mimics the appearance of flames from burning straw in the fields. If it instead rivals the flame of a bright hearth, authors have named this phenomenon the Altar (*Ara*), because a similar glow was seen on the altars of the ancients when sacrifices were lit. When the length of the exhalation is greater than its width, it takes the form of a beam (*Trabs*). Furthermore, when it is stretched out long and thin, it has the shape of a burning spear (*Hasta*). But when the ignitions and sparks are not joined together nor positioned along a straight line, but are instead scattered and dissipated—such that the first part of the exhalation is lit, then other portions are ignited successively as the previous ones are extinguished, separated by a small distance and not in a straight line—then they seem to mimic the tracks of jumping goats (*Caprae Saltantes*).

Finally, if the exhalation and its subsequent inflammation do not proceed along a straight line but fly here and there, it takes on the appearance of a falling or "flying" star; as one "star" seems to be extinguished, the inflammation appears to hurry toward the next particle of the exhalation. The appearances of several of these are shown in the following Figure I, where the shapes of the Altar, the Beam, the Spear, and the Jumping Goats are visible.

Since the material, substance, and nature of falling stars and the aforementioned fiery phenomena are similar to those of comets, it seems naturally consistent that we should discuss comets as monstrous apparitions of the heavens. Comets are, by nature, quite hot and dry; indeed, they signal that the air in the place and region they begin to illuminate with their splendor is becoming hotter and drier.

Therefore, philosophers and investigators of natural things, following the mind of Aristotle, proceed with probable reasons to explain the creation of comets. First, they assume three things that were previously laid down as the foundations of this meteorological doctrine. The first is that beneath the celestial bodies there is an exhalation, which they are accustomed to calling either the *hypocauma* or "the fire." The second is that this substance, and the air joined to it, is agitated by a circular motion. Finally, because of this motion, this exhalation is usually ignited—though not the whole of it, but only that portion which was suitable for receiving the fire; the other parts are then inflamed in turn. From this process, the different varieties of so many fiery phenomena usually take their origin.

With these points recalled to mind, they attribute the true origin of comets to the fiery power of the Heaven or of some star, according to whose motion those exhalations are carried. Next, they trace comets back to the exhalation as their material cause, which rises incessantly day by day from the drier parts of the earth into the higher regions. Thus, as the previous exhalation is consumed, a fresh and new one is ready to take its place. Because this process persists for some time, a comet is nothing other than an exhalation ignited and inflamed in a successive manner.

However, if such an ignited exhalation surrounds a star like hair or curls, we can rightly call this exhalation a "comet"—that is, a hairy star. Furthermore, when the exhalation is arranged near a star in the manner of a beard, we can call it a *Pogonias*. Among the Greeks, *kometes* (κομήτης) means hairy or long-haired; indeed, this word is used absolutely by Aristotle for *aster kometes* (ἀστὴρ κομήτης), a hairy star with flowing locks or curls. Since *pogonias* (πωγωνίας) is translated as "bearded," it is no wonder if comets are sometimes called *pogonias asteres* (πωγωνίαι ἀστέρες). Ptolemy, however, called comets *ta phthartika astra* (τὰ φθαρτικὰ ἄστρα), namely, "corruptible" or elementary stars.

Many authors, and most notably Pliny, established nine types of comets