Lumen

by Camille Flammarion

A belated courier.

Quærens. In other words, the ray of light is like a courier who brings despatches from a distant country, and having been nearly seventy-two years on the way, his news is of events that occurred at the time of his departure seventy-two years ago.

Lumen. You have divined the mystery. Your illustration shows me that you have lifted the veil which shrouded it. In order to be still more exact, the light represents a courier who brings, not written news, but photographs, or, strictly speaking, the real aspect of the country from whence he came. We see this living picture such as it appeared, in all its aspects, at the moment when the luminous rays shot forth from the distant orb. Nothing is more simple, nothing more indubitable. When we examine the surface of a star with a telescope we see, not the actual surface as it was at the time of our observation, but such as it was when the light was emitted from that surface.

Quærens. This being so, if a star, the light of which takes ten years to reach us, were to be annihilated to-day, we should continue to see it for ten years, since its last ray would not reach us before ten years had elapsed.

We see the past, not the present, aspect of the stars.

Lumen. It is precisely so. In short, the rays of light that proceed from the stars do not reach us instantaneously, but occupy a certain time in crossing the distance which separates us from them, and show us those stars not as they are now, but such as they were at the moment in which those rays set out to transmit the aspect of the stars to us. Thus we behold a wondrous transformation of the past into the present. In the star we observe we see the past, which has already disappeared, while to the observer it is the present, the actual. Strictly speaking, the past of the star is positively the present of the observer. As the aspect of the worlds change from year to year, almost from day to day, one can imagine these aspects emerging into space and advancing into the infinite, and thus revealing their phases in the sight of far-distant spectators. Each aspect or appearance is followed by another, and so on in endless sequence. Thus a series of undulations bears from afar the past history of the worlds which the observer sees in its various phases as they successively reach him. The events which we see in the stars at present are already past, and that which is actually happening there we cannot as yet see. Realise to yourself, my friend, this presentation of an actual fact, for it is of importance to you to comprehend the precession of the waves of light and to understand the essential nature of this undoubted truth. The appearance of things, borne to us by light, shows us those things not as they are at present, but as they were in that period of the past which preceded the interval of time needed for the light to traverse the distance which separates us from those events.

We do not see any of the stars such as they are, but such as they were when the luminous rays that reach us left them.

The planet Earth as seen from afar.

It is not the actual condition of the heavens that is visible, but their past history. Moreover, there are distant stars which have been extinct for ten thousand years, but which we can see still, because the rays of light from them had set out before they were extinguished. Some of the double stars, the nature and movements of which we seek with care and toil, ceased to exist long before astronomers began to make observations. If the visible heavens were to be annihilated to-day we should still see stars to-morrow, even next year, and for a hundred years, a thousand years, and even for fifty and a hundred thousand years, or more, with the exception only of the nearest stars, which would disappear successively as the time needed for their luminous rays to reach us expired. Alpha of Centaur would go out first, in four years, Sirius in ten years, and so on.