— Immanuel Kant
Free translation, as quoted by Edwin Powell Hubble, The Realm of the Nebulae (1936)
An Original Theory or New Hypothesis of the Universe (1750)
Kontextus: I come now to another part of my system, and because it suggests a lofty idea of the plan of creation, it appears to me as the most seductive. The sequence of ideas that led us to it is very simple and natural. They are as follows: let us imagine a system of stars gathered together in a common plane, like those of the Milky Way, but situated so far away from us that even with the telescope we cannot distinguish the stars composing it; let us assume that its distance, compared to that separating us from the stars of the Milky Way, is the same proportion as the Milky Way is to the distance from the earth to the sun; such a stellar world will appear to the observer, who contemplates it at so enormous a distance, only as a little spot feebly illumined and subtending a very small angle; its shape will be circular, if its plane is perpendicular to the line of sight, elliptical, if it is seen obliquely. The faintness of its light, its form, and its appreciable diameter will obviously distinguish such a phenomenon from the isolated stars around it.
We do not need to seek far in the observations of astronomers to meet with such phenomena. They have been seen by various observers, who have wondered at their strange appearance, have speculated about them, and have suggested some times the most amazing explanations, sometimes theories which were more rational, but which had no more foundation than the former. We refer to the nebulæ, or, more precisely, to a particular kind of celestial body which M. de Maupertius describes as follows:
"These are small luminous patches, only slightly more brilliant than the dark background of the sky; they have this in common, that their shapes are more or less open elipses; and their light is far more feeble than that of any other objects to be perceived in the heavens."
... It is much more natural and reasonable to assume that a nebula is not a unique and solitary sun, but a system of numerous suns, which appear crowded, because of their distance, into a space so limited that their light, which would be imperceptible were each of them isolated, suffices, owing to their enormous numbers, to give a pale and uniform luster. Their analogy with our own system of stars; their form, which is precisely what it should be according to our theory; the faintness of their light, which denotes an infinite distance; all are in admirable accord and lead us to consider these elliptical spots as systems of the same order as our own—in a word, to be Milky Ways similar to the one whose constitution we have explained. And if these hypotheses, in which analogy and observation consistently lend mutual support, have the same merit as formal demonstrations, we must consider the existence of such systems as demonstrated...
We see that scattered through space out to infinite distances, there exist similar systems of stars [nebulous stars, nebulæ], and that creation, in the whole extent of its infinite grandeur, is everywhere organized into systems whose members are in relation with one another.... A vast field lies open to discoveries, and observations alone will give the key.