Page:A short history of astronomy(1898).djvu/170

124 far off that any motion due to this cause was too small to be noticed. If, for example, the earth moves in six months from to, the change in direction of a star at  is the angle , which is less than that of a nearer star at ; and by supposing the star  sufficiently remote, the angle  can be made as small as may be required. For instance, if the distance of the star were 300 times the distance, i.e. 600 times as far from the earth as

the sun is, the angle would be less than 12', a quantity which the instruments of the time were barely capable of detecting. But more accurate observations of the fixed stars might be expected to throw further light on this problem.