Page 171 - 89 history of astronomy_opt

pared with the best modern catalogues, his
ˆ
probable error in right ascension is only A l
ˆ
24”, 1, and in declination only A l 25”, 9.
Clocks of a sort had been made, but Ty-
cho Brahe found them so unreliable that he
seldom used them, and many of his position-
measurements were made by measuring the
angular distances from known stars.
Taking into consideration the absence
171