Observatio & demonstratio cometae aetherei, qui anno 1577 et 1578 constitutus in sphaera veneris, apparvit, cum admirandis eius passionibus, varietate scilicet motus, loco, orbe, distantia à terrae centro, &c. adhibitis demonstrationibus geometricis & calculo arithmetico, cuiusmodi de alio quoquam cometa nunquam visa est

The motion of the Comet is not wandering, but defined. For while other Comets of past centuries were observed wandering with uncertain motions, pushed here and there, as happens when exhalations are naturally snatched from the earth into the air and ignited there, it is certain that this one did not deviate by a hair's breadth from its path, its invariable orbit—which it was established to possess—and the circle of the ultimate sky under which it began to move, during the whole time of its appearance, but was circumscribed by most certain laws no differently than any other star, as will be proved below.

Unheard-of magnitude of the Comet. The magnitude of this Comet, and the unusual and unheard-of length of its hair, swept through the space of an entire dodecamerium meaning a zodiacal sign, or 30 degrees, that is 30 degrees and more. With what astonishment all nations were horrified by the long beard of the Comet of the year 1531, which it extended for 20 degrees, is testified by the Poet, who was not afraid to say:

The whole earth subject to the Lycaonian pole
Denies having seen one like this in previous years.
From the setting of the sun it scattered flames toward the rising,
Covering twice ten degrees of space.

What must be said of this one, which exceeds that one by half and more? Certainly, by its dire radiance and magnitude, it was so terrible to all men that many, seized by admiration for it, thought of repentance by which they might deprecate the imminent wrath of God and the approaching punishments, in which, if they had persisted, there is no doubt that God, out of His immense goodness, would have averted the evils He had proposed. But since what they feared did not appear, many (alas, the evil) soon failing, returned to their accustomed ways, as the Apostle speaks, like a dog to its vomit.

Color of the Comet. This Comet shone with a very dire color, not indeed purple or glowing blood-red, which was the usual color of most other Comets, nor white or silvery, but a whitish, lucid, or pale yellow, which it later converted in December into a dull or dark and blackish leaden hue. Some try to persuade us that it appeared reddish at the beginning: but that diversity happens due to the unsuitable density of clouds and vapors, through which the setting sun similarly appears purple: for where the sky was a little clearer, such things were not noticed.

After the 20th of December, until it had entirely burned out, a certain brighter whiteness shone in the middle of the head (which was surrounded on all sides by hairs or rays), like a small silver star, more luminous than the rest of the body.

The tail of the Comet. It also twisted its hair or tail far away from the opposite of the sun in an oblique and almost sickle-shaped path, whereas it is reported that other Comets placed it directly opposite the sun.