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

commemorate them. For this same reason, Most Illustrious Prince, most clement Lord, I most submissively offer Your Highness these same lucubrations of mine, supplicantly praying that you may be willing to look upon not these, however small they may be (for to adorn greater things, to demonstrate the affections of my mind, is not in my power), but my very mind, which dedicates and devotes all its things, and itself, to Your Highness.

In this writing, I offer Your Highness the admirable phenomena of this admirable Comet. For I have attempted to elucidate this alone, that from exquisite and certain observations, I might explain its true motions, which it kept from the first day of its appearance until its extinction, bound by the most certain astronomical laws no less than has been discovered regarding any other star. For it had sought a seat for itself, not among the elements, but in the sphere of Venus in a certain orbit, the circumduction of which it also followed with such observance that from it its motion and place in its circle under the starry sky, as well as its distance from the earth and the center of the world, can be computed and known at any moment, just as I hope that all these things, constructed from true observations and fortified so well with Geometric demonstrations and Arithmetical calculation, cannot be eluded or overturned by anyone. In the descriptions of other Comets seen before, I do not find such things. But it is to be deplored all the more that this same thing was not done by others in the explanations of this Comet, so that indeed in this way we might illustrate with our observations what we have received from the ancients, and render the contemplations of nature more open. But not without pain do I see that most Astrologers neglect this entirely as idle and unworthy, in which the effects of the Comet might be written, even though they undoubtedly must deviate from the truth of judgments, who wander through the whole sky regarding its state, place, motion, and distance from the earth.

Nevertheless, I must confess here that I have not entirely satisfied the expectation of many into whose hands these writings of mine will fall. For although I have compiled what an Astronomer can say about this Comet, yet what it portends, I have noted only as conjectures, not flowing from the fountains of Astrology, but derived from elsewhere. However, I hope that I bring a cause for that matter not unworthy of pardon. For even though I have made abstract and concrete Mathematics somewhat familiar to me until now, in the concrete, to which the considerations of celestial motions are subject, I have applied myself to Astronomy rather than Astrology. For since from the multiple writings of other learned men...