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

degrees, and somewhat more, in width. For that width exceeded twice the distance of the stars in the horns of Capricorn on either side: now this is two and a half degrees. The end of the longitude could not be marked with certainty, since the hair or rays of the hair gradually faded and attenuated, failing near the head of Capricorn. It was also evident in its appearance that obscure rays like little flames emerged from the head toward the south, not a little distant from the tail, yet much shorter and darker than the entire rest of the tail. These rays reached as far as the head of the constellation on November 12th.

From what has been said, it can easily be demonstrated that the tail of this Comet was not collected in one point, nor even diametrically opposite the Sun, but was twisted away by a long interval from its direct opposition, when otherwise it should have been far more northern than the head. Just as this same thing can be seen in the figure on the first page, in which the location of the Comet is depicted for several days, to which the location of the Sun for the same days is added, with which the head of the Comet is connected by dotted lines, to demonstrate the aversion of the tail from the opposite of the Sun.

Hence it is also manifest that the same tail exceeded the length of the whole sign.

This position and this obliquity of the tail remained unchanged until the end. For on November 17th, when the head was closest to the star which was in the knees of Antinous, the southern edge of the tail grazed the bands of Aquarius, but those obscure little flames belonged almost to the eastern horn of Capricorn. On December 2nd, when the head of the Comet approached the stars in the nostrils of the little horse, the tail was led through the mouth of Pegasus, and those dark little flames descended to the other small stars of the little horse. On December 6th, the tail left that which is in the mouth to the south, and extended as far as the stars in the neck of Pegasus, failing a little below the same, but those dark rays inclined beyond the mouth. On December 31st, the tail was led below the stars of the breast of Pegasus, by almost twice the space that falls between those stars.

After November 12th, it was found to diminish just as much in magnitude of body and clarity of radiance as it did in velocity of motion, though not equally. For on December 6th it was seen to have barely diminished by a third, but still to exceed 20 degrees, from the fact that it touched the stars in the neck of Pegasus. But afterward it diminished notably day by day, so much so that the end of the tail could hardly be seen in the consequence (as was observed in the head), but as much as the head proceeded forward, so much was the tail curtailed behind. Hence, on January 6th of the year 1578, it equaled only 6 degrees in longitude, and on the 8th of the same, barely 3 degrees.