Page:The Music of the Spheres.djvu/113

 But astronomers write it this way—"It has taken only 800 years for Arcturus to describe a space equal to the apparent diameter of the moon," for the stars are so very distant that most of them do not seem to change their places in the heavens even in the course of many thousands of years.

Amazing as the speed of Arcturus appeared to astronomers, they later discovered a star of the 8th magnitude in the southern hemisphere with even a greater proper motion. This star has moved the distance of the diameter of the moon in 220 years, which means that it moves over a hundred times faster than the average star. But the late Professor Barnard of the Yerkes Observatory had the distinction of discovering a star with the largest proper motion known. The average star does not exceed one minute of arc in a thousand years but Professor Barnard's "runaway star" has the amazing proper motion of 10.3 seconds a year. In that length of time it travels twice as far as the average star does in a century!

Scientists accomplish many wonderful, and most remarkable, deeds. Even the heroes who lived in the vivid minds of the ancient peoples dwindle into insignificance beside these men with their calm patience and brilliant seeking minds.

Professor Michelson has now invented a new method of measuring the angular diameter of the more distant stars. This is by means of an instrument called the "interferometer" which is attached to the 100-inch reflector of the Mount Wilson Observatory. Measurements of the angular diameter of Arcturus with the interferometer combined with the knowledge of its distance give us