Page:Popular Science Monthly Volume 32.djvu/66

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56
THE POPULAR SCIENCE MONTHLY.

recognized, and a keen eye will perceive that Alpha really consists of two stars. They are about six minutes of arc apart, and are of the third and the fourth magnitude respectively. These stars, which to the naked eye appear almost blended into one, really have no physical connection with each other, and are slowly drifting apart. The ancient astronomers make no mention of Giedi being composed of two stars, and the reason is plain, when it is known that in the time of Hipparcus

PSM V32 D066 Andromeda cygnus and pegasus.jpg

Map 2.

as Flammarion has pointed out, their distance apart was not more than two thirds as great as it is at present, so that the naked eye would not have detected the fact that there were two of them; and it was not until the seventeenth century that they got far enough asunder to begin to be separated by eyes of unusual power. With