De cometis

Before the rising of the sun, it judged the place of the north from whence it was accustomed to blow. This diversity of the tail in position arose from the diurnal motion which the comet had, from the motion of the container following the primum mobile the first moved sphere, which is always from the east to the west. But by its own motion, the extremity of the tail, although slower than the head of the comet, still always described a parallel against the succession of signs toward the west, from the beginning of Libra until the middle of Taurus, going under the feet of the Wreather Bootes through the Great Bear, approaching Perseus, through which it went around the Pleiades to the tail of Aries, almost into the middle of Taurus. Whence it is evident that both the head and the tail of the comet went toward the west and never toward the east, not only by diurnal motion but also by its own.

On the distance of the comet from the earth

Those who know the reasons of geometry and arithmetic will least disagree with those things which are demonstrated from the positions of Ptolemy, by which he demonstrated in the Almagest Ptolemy's foundational work on astronomy that the concave of the sphere of the moon is distant from the center of the earth by thirty-three times as much as it is from the same center to the surface of the earth. The semi-diameter of the earth, as can be gathered, contains almost nine hundred and sixteen miliaria teutuica German miles. And by him, as Alfraganus an Arab astronomer says, the distances of the stars from the earth are reasoned by the twenty-first division. Considering, therefore, the maximum diversity of the aspect of the head of the comet from the star Alranick unidentified star, perhaps an archaic reference near to it, which, with all deformities reduced according to possibility, could not be perceived as greater than six degrees with instruments ordained for this, it follows necessarily that the body of the comet was distant from the surface of the earth at a ninefold distance to the semi-diameter of the earth, which is at least eight thousand and two hundred miles. It was placed, therefore, in the superior part of the supreme region of the air and not in the fire, assuming a tenfold quantity of the commensuration of the elements as the philosopher determines in the second book of De Generatione On Generation and Corruption.

ON THE MAGNITUDE OF THE COMET.

Since the diameter of the head of the comet would chord eleven minutes of a great circle, as was perceived by instruments, whose chord of minutes is eleven minutes and almost a half, that chord, as has been said in the first part, should be multiplied by the distance of the comet from the earth, namely eight thousand and two hundred miles, and it will produce ninety-four thousand and three hundred, which should be divided by the total sine, namely three thousand and six hundred minutes, and there will result twenty-six miles, which is the quantity of the diameter of the head of the comet. The comas the glowing gaseous envelope around the head coming out from everywhere from the head of the comet corded almost thirty-four minutes. Therefore, their diameter was almost eighty-one miles.

ON THE LENGTH OF THE COMET

The tail, however, in its greater length when the comet was around the stars of the Northern Fish, and extending the tail almost to the Pleiades, distant from the head of the comet by thirty-five degrees, corded about thirty degrees. Therefore, its length was more than four thousand miles. Nevertheless, its common length in the preceding days was two thousand and five hundred miles. But if it had not been distant from the earth except by the quantity of the semi-diameter of the earth, its length would still have been four hundred and sixty miles. To bring the particular mathematical demonstrations of all these things would be lengthy and very tedious.