colophon is the vignette "Svspiciendo Despicio," with the words underneath "Uranibvrgi In Insula Hellesponti Danici Hvenna imprimebat Authoris Typographus Christophorus Weida. Anno Domini mdlxxxviii."
The book is divided into ten chapters. The first contains most of the observations of the comet; the second deduces new positions for the twelve fixed stars from which the distance of the comet had been measured. Tycho mentions that while the comet was visible he had not yet any armillæ, and he therefore carefully placed a quadrant in the meridian, and thus determined the declination of the star, and by the time of transit (through the medium of the moon and the tabular place of the sun) also the right ascension. He does not give any particulars about the observations and method, but he goes through the computations of the latitude and longitude of each star from the right ascension, declination and the point of the ecliptic culminating with the star. In a note at the end of the chapter he gives improved star places from the later observations with better instruments and methods, and, as might be expected, these later results are really much better than those found in 1578.[1] In the third chapter the longitude and latitude of the comet for each day of observation are deduced from the observed distances from stars; but though he gives diagrams of all the triangles, and gives all the numerical data, the trigonometrical process is not shown. In the fourth chapter the right ascensions and declinations of the comet are computed from the longitudes and latitudes.[2] The fifth deals with the deter-
- ↑ In the above-mentioned paper Woldstedt compares the two sets of positions with modern star places (Åbo or Pond with proper motions from Bessel's Bradley or Åbo). The means of the errors of Tycho's places, irrespective of sign, are in longitude and latitude, for the older positions, 4′.8 and 1′.1, for the later ones, 1′.4 and 1′.5. About the methods by which these positions were found, see Chapter XII.
- ↑ By the method of Al Battani, which employs the point of the equator having the same longitude as the comet. Delambre, Astr. du Moyen Age, p. 21.
