THE STARS OF THE SECOND MAGNITUDE
Then come the stars of the second magnitude, of which there are fifty-nine. The stars of the Great Bear (with the exception of δ, which is of third magnitude), the Pole-Star, the chief stars in Orion (after Rigel and Betelgeuse), of the Lion, of Pegasus, of Andromeda, of Cassiopeia, are of this order. These, with the former, constitute the principal outlines of the constellations visible to us.
Then follow the third and fourth magnitudes, and so on.
The following table gives a summary of the series, down to the sixth magnitude, which is the limit of visibility for the unaided human eye:
| 19 | stars of first magnitude. |
| 59 | of second magnitude. |
| 182 | of third magnitude. |
| 530 | of fourth magnitude. |
| 1,600 | of fifth magnitude. |
| 4,800 | of sixth magnitude. |
This makes a total of some seven thousand stars visible to the unaided eye. It will be seen that each series is, roughly speaking, three times as populated as that preceding it; consequently, if we multiply the number of any class by three, we obtain the approximate number of stars that make up the class succeeding it.
Seven thousand stars! It is an imposing figure, when one reflects that all these lucid points are suns, as enormous as they are potent, as incandescent as our own (which exceeds the volume of the Earth by more than a million times), distant centers of light and heat, exerting their attraction on unknown systems. And yet it is generally imagined that millions of stars are visible in the firmament. This is an illusion; even the best vision is unable to distinguish stars below the sixth magnitude, and ordinary sight is far from discovering all of these.
Again, seven thousand stars for the whole Heavens makes only three thousand five hundred for half the sky. And we can only see one celestial hemisphere at a time. Moreover, toward the horizon, the vapor of the atmosphere veils the little stars of sixth magnitude. In reality, we never see at a given moment more than three thousand stars. This number is below that of the population of a small town.