The Author. You must bear in mind that the word magnitude signifies in astronomy the opposite of that which it expresses. The more luminous a star appears to us, the nearer it is to us; the paler and less visible, the farther it is away. The brilliance diminishes in proportion as the figure increases. This is an introversion of terms, sufficiently exceptional to be taken note of, and it ought to be remembered, for fear of mistakes. Hitherto we have considered only stars of the first and second magnitudes. Those of the third, fourth, fifth, and sixth, lead us to the contemplation of such immense distances, that the unit which we have adopted, enormous as it is, is no longer of use. The instruments of celestial observation which may be applied to the examination and measurement of stars of the first and second magnitudes, do not serve for stars of the third and following magnitudes, and, because the small visible diameter of those stars make them appear mere specks of light, measuring instruments are equally inapplicable to them. In estimating the distances of the stars after the third magnitude, a method of comparison, based on the amplifying power of the telescopes successively used, is employed. I cannot enter into details of this method, which we owe to Sir William Herschel, but must content myself with explaining its results, which are as follows in the case of stars of the sixth magnitude. From certain stars of that class, light would take 1042 years to reach us: from others it would take 2700. After the sixth magnitude, the stars can only be discerned by the aid of the telescope, and their distances become perfectly stupefying in immensity. Certain of these telescopic stars are so far from the earth, that their light can only reach us in 5000, and even 10,000 years after it leaves the luminous centre. From the stars of the last category (fourteenth magnitude), light would take 100,000 years to reach the earth, supposing it to travel at the same rate as the light of our sun, i.e., 77,000 leagues per second.
Theophilus. But, if we are to accept the results of the labours of recent naturalists, man exists on the earth only within 100,000 years, and some of those stars may have been extinct during all that time, so that the human race may have been contemplating stars no longer in being for 100,000 years. To what strange consequences does such a science lead us!
The Author. Yes, the luminous rays which these stars send us from the deepest depths of space may perhaps be emanations from solar systems no longer in existence. The present shows us only the past. There may be stars so profoundly lost in immensity, that their light has not yet had time to reach us. They exist, but we cannot see them, not because the telescope could not discover them, but because thousands of centuries are required for the journey of their luminous rays to our earth, and those thousands of centuries have not yet elapsed; so that this grand spectacle is reserved, in that awfully remote future, for our descendants.
And now, my friend, will you not acknowledge with me, that the universe, considered merely by the distances which separate us from the stars, and the stars from each other, is truly the Infinite?
Theophilus. Yes, it is the Infinite which unfolds itself before my eyes. Let me breathe a moment.
The Author. If we contemplate the number of the stars, we shall also have the perspective of the Infinite. It is easy to reckon those of the first magnitude, i.e., the nearest to us. They are 20. Those of the second magnitude are 65; of the third, 170. The number of the stars increases as their visibility diminishes, in a very rapid proportion. The number of stars of each class of visibility, in apparent magnitude, is three times greater than that of the stars of the preceding class. There are 500 stars of the fourth, 1500 of the fifth, 4500 of the sixth magnitudes. The stars visible by the naked eye are 6000 in number. A practised eye can succeed in counting the 6000 stars in the two hemispheres.
Fig. 6.—A Corner of the Constellation of Gemini.
But the telescope enables us to push the numbering of the suns much farther: it opens up to us the depths of the heavens. Instead of the small number of stars which our eyes can see, it shows us a myriad of others, so thickly thronged together that they seem to cover the sky with fine silver sand. Here, for instance (fig. 6), is the aspect which one corner of the constellation of Gemini presents to the naked eye. And here is the same portion of the sky seen by the telescope. By the aid of this wonderful instrument stars of the thirteenth and fourteenth magnitudes have been distinguished. The number of stars of the twelfth magnitude is 9,556,000, which, joined to the number of the same stars proper to the preceding categories, gives a total of more than 14,000,000. In the third magnitude, a total number of 42,000,000 of stars is counted. Thus, reckoning those visible to the naked eye, and by the telescope, we have 56,000,000 of suns, and we stop at this number only because the telescope does not enable us to see smaller stars than those of the fourteenth magnitude. But, let the telescope be brought to greater perfection, and the whole region of the sky will be seen to be covered with this silver sand, with this diamond dust, of which each grain is a sun. And such will be the accumulation of these suns, in the depths of space, that nothing will be seen on the field of the telescope but a luminous network, formed by the agglomeration of the suns, which will appear to touch each other.
