deal to say about the star, but most of his distance measures are upwards of a degree wrong. On the other hand, Michael Mœstlin, the teacher of Kepler, though he possessed no instruments, determined the place of the star with fair accuracy simply by picking out four stars so placed that the new star was in the point of intersection of two lines drawn through two and two of them. As the star did not move relatively to these four stars during the daily revolution of the heavens (of which he assured himself by holding a thread before the eye, so that it passed through the three stars), Mœstlin concluded that it had no parallax, and that it was situated among the fixed stars, whose distance Copernicus, of whom he was a follower, had shown to be extremely great. Digges tried the same method, using a straight ruler six feet long, which he first suspended vertically until he found two stars which were in the same vertical as the new star; six hours afterwards he tried again, holding the ruler in his hand, whether the three stars were still in a straight line. He found the star to be exactly in the point of intersection of the line joining β Cephei and γ Cassiopeæ, and the line joining ι Cephei and δ Cassiopeæ, and concluded that it could not have a parallax amounting to 2′. Tycho afterwards computed the place of the star from these data, using his own accurate positions of the four stars, and found the longitude only 2′ greater and the latitude 12′; greater than what he had deduced from his own observations.[1] Digges had hoped to test the Copernican theory of the motion of the earth by trying whether the star had an annual parallax, but he could find none.
- ↑ Digges, l.e., chapter x., fol. K 3. By a mistake he says that the two lines join δ Cassiopeæ, β Cephei, and ι Cephei, γ Cassiopeæ. Tycho remarks that one can see at a glance that these two lines do not intersect each other between the stars, but pretending not to see that it is merely a lapsus calami, he gravely calculates places from these data, using his own distances, and of course gets absurd results (Progymn., p. 681), after which he interchanges the stars, and gets the correct result given above.
