tudes gave the same latitude (for Heridsvad and Göggingen) as other stars gave; and the fourth is, that observations at far-distant places gave results in good accordance inter se, as, for instance, his own and those of Munosius at Valencia. As Tycho has so often referred to the parallax of the moon, he verifies at the end of this chapter the value of Copernicus by computing the lunar parallax from six observations, three on the meridian and three at the nonagesimal point, where there is no parallax in longitude.
In the seventh and last chapter of the second part of the book Tycho attempts to calculate the diameter of the new star. He first recounts the crude ideas of his predecessors as to the diameters of the planets and fixed stars, on which he did not improve very much himself. He did not, however, place all the fixed stars at the same distance just beyond the orbit of Saturn, and he suggested that the fainter stars are probably at a far greater distance than the brighter ones, though even if they were at the same distance it would not follow that all the stars which we consider as belonging to one magnitude were equal in size, as Sirius and Vega are much larger than Aldebaran, which again is larger than Regulus.[1] The apparent diameter of the sun Tycho had, in 1591, measured "through a canal 32 feet long," and in this way he found that at the apogee the diameter was barely 30′, and at the perigee slightly above 32′.[2] The instrument was, according to Kepler, a screen on which the image of the sun fell through a small opening, and the "canal" must have been added merely to exclude stray light.[3] The diameter of the moon Tycho generally
