This latter
observer saw it on this occasion stand out against the background of
the sky as of a pale ashen green, while on February 28th following, it
seemed to him of a pale reddish gray, like the color of the eclipsed
moon.
That the latter body should send to us from her nocturnal shadows
sufficient light to be visible is easily explicable, since she is then
flooded with earth-light reflected on her from a surface thirteen and
one-half times greater than her own, and probably casting on her an
illumination transcending our full moonlight in the same proportion.
But the secondary light of Venus admits of no such explanation, since
earth-light on her surface, diminished by 1/12000th part compared to
what it is on that of the moon, would be quite insufficient to render
her visible to our eyes. The phenomenon was therefore adduced as an
argument for the habitability of the planets by Gruithuisen, of the
Munich Observatory, who, writing early in this century, suggested that
the ashen light of Venus might be due to general illuminations in
celebration by her inhabitants of some periodically recurring
festivity, The materials for a flare-up on so grand a scale would, he
thought, exist in abundance, as he conjectured the vegetation of our
planetary neighbor to be more luxuriant than that of our Brazilian
forests.
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