This page has been validated.
PLEASURES OF THE TELESCOPE.
509
power of such an instrument divides the star into two twinkling points. They are about two and a quarter minutes of arc apart, and exceptionally sharp-sighted persons are able to see them divided
![](http://upload.wikimedia.org/wikipedia/commons/thumb/b/b1/PSM_V47_D523_Wonders_of_the_night_sky_map_17.jpg/500px-PSM_V47_D523_Wonders_of_the_night_sky_map_17.jpg)
Map No. 17.
with the naked eye. Now take the three-inch telescope with a moderate power, and look at them. Each of the two stars revealed by the opera glass appears double, and a fifth star of the ninth magnitude is seen on one side of an imaginary line joining