Transit of Venus

“ Besides the advantage of having a dial-face like the sun’s on which thus to determine positions, the transit method deals with Venus when at her nearest, or about 25 million miles from us, instead of the sun at his greater distance of from 901⁄2 to 931⁄2 millions of miles. Yet we do not get the entire advantage of this relative proximity of Venus. For the dial-face—the sun, that is—changes its position too—in less degree than Venus changes hers, but still so much as largely to reduce her seeming displacement. The sun being further away as 92 to 25, is less displaced as 25 to 92. ”

“ Doubtless, however, we must wait for the transit of Venus in 1874 before forming a final decision as to the estimate of the sun’s distance which is to take its place in popular works on astronomy during the next century or so. Nothing but an unlooked-for combination of unfavourable circumstances can cause the failure of our hopes. ”

“ The instant their bright flash disappears, the observer knows that the planet has so moved as to intercept the rays of light, and is just in contact. Their reappearance, at the proper time, on the other side of the sun, will indicate the instant when Venus will have quitted the disk and the transit is over. ”

“ It is not, however, to be supposed that every eight years the planets will again resume the same position with sufficient precision for a regular eight-year transit interval. It is only approximately true that thirteen revolutions of Venus are coincident with eight revolutions of the earth. ”

“ As there is no appreciable body nearer to us than the moon, we can never see anything in transit across her disc. But since the planets Venus and Mercury are both nearer to us than the sun, they will occasionally be seen to pass across his face, and thus we get the well-known phenomena called Transits of Venus and Transits of Mercury.
As the satellites of Jupiter are continually revolving around him, they will often pass behind or across his disc. Such occultations and transits of satellites can be well observed in the telescope. ”

“ One thing I request: let no severe Cato be seriously offended with our follies; for, to speak poetically, what young man on earth would not, like ourselves, fondly admire Venus in conjunction with the sun, pulchritudinem divitiis conjunctam?"
Many years passed before another transit of Venus took place. This was the transit of 1761, and it affords striking evidence of the interest with which, even at this early epoch, astronomers regarded the transits of Venus, that Dr. ”

“ It is open, at least to the writers of the interplanetary romances now so popular, to imagine that on Venus, life, while encompassed with the serenity that results from the circular form of her orbit, and the unchangeableness of her climates, is richer, warmer, more passionate, more exquisite in its forms and more fascinating in its experiences, keener of sense, capable of more delicious joys, than is possible to it amid the manifold inclemencies of the colder earth. ”

“ While these clouds render the planet surprisingly lustrous to our eyes, they must, of course, keep the globe beneath them most of the time in shadow. It is a source of keen regret that the surface of Venus can not be seen as clearly as that of Mars, for, a priori, there is rather more reason to regard Venus as possibly an inhabited world than any other of the Earth's sister planets, not excepting Mars. ”

“ A space traveller hovering several million miles directly above the Sun would thus see Venus as almost stopped in its rotation and possibly turning very slowly clockwise. All the other planets of our system including the Earth, rotate counterclockwise, except Uranus, whose axis is almost parallel to the plane of its orbit, making it seem to roll around the Sun on its side. ”

“ As she comes nearer to inferior conjunction, and hence nearer to us, she becomes a thinner and thinner crescent, and as she goes from inferior to superior conjunction these phases are repeated in reverse order. We see less than half of her face when she is at her greatest brilliancy, a phase which usually occurs when she is about forty degrees from the sun, as she is a few weeks before and after inferior conjunction. A very small glass will show the phases of Venus. They have occasionally been seen without artificial aid to vision by an exceptionally good eye. ”

“ You know already how dense the atmosphere of Venus is. It follows that balloons, and all sorts of machines for aerial navigation, can float much more easily here than over the earth. I was prepared to find the inhabitants of Venus skilled in such things, and I'm not surprised by what we see."
"Venus with wings!" cried Jack. "Now, Edmund, that sounds more like it. I guess we've struck the right planet after all." ”

“ We do not have to depend upon the spectroscope for evidence that Venus has a dense atmosphere, for we can, in a manner, see her atmosphere, in consequence of its refractive action upon the sunlight that strikes into it near the edge of the planet's globe. This illumination of Venus's atmosphere is witnessed both when she is nearly between the sun and the earth, and when, being exactly between them, she appears in silhouette against the solar disk. ”

“ Gradually the black spot steals in front of the sun, until, after nearly half an hour, the black disc is entirely visible. Slowly the planet wends its way across, followed by hundreds of telescopes from every accessible part of the globe whence the phenomenon is visible, until at length, in the course of a few hours, it emerges at the other side.
It will be useful to take a brief retrospect of the different transits of Venus of which there is any historical record. They are not numerous. Hundreds of such phenomena have occurred since man first came on the earth. ”

“ For those Spots I could very well observe for a whole night together, during the opposition of those Planets to the Sun: I could consider their Motion for the space of several hours; and at last, seeing them return regularly to the same place, I could judge whether they were the same spots or not, and in how much time they absolv'd their Relation. But it was not so here with the Apparences in Venus; for one sees them but for so small a time, that it is far more difficult, certainly to know, when they return to the same place. ”

“ Then the crescent becomes gradually thinner, and next will follow a brief period of invisibility before the appearance of Venus as the morning star. It seems at first a little strange that Venus when brightest should not be full like the moon, which in similar circumstances is, of course, a complete circle of light. The planet, however, has a very marked crescent-shaped form in these circumstances. But at this time the planet is so near us that the gain of brilliancy from the diminution of distance more than compensates for the small part of the illuminated side which is turned towards us. ”

“ And as Venus glowed with increasing splendor in the serene evenings of June, she continued to be mistaken for some petty artificial light instead of the magnificent world that she was, sparkling out there in the sunshine like a globe of burnished silver. Yet Venus as an evening star is not so rare a phenomenon that people of intelligence should be surprised at it. ”

“ He fell silent, while the viso-screen began to show a crowded space port on Venus, and a gigantic passenger spacer up-tilted in its cradle.
They watched the parabola it made in its trajectory as it flashed into space and then fell into orbit there beyond the planetary attraction of Venus. On the three-dimensional viso-screen it was uncannily real. ”

“ A man removed to Venus would, consequently, find himself perceptibly lighter than he was at home, and would be able to exert his strength with considerably greater effect than on his own planet. But the difference would amount only to an agreeable variation from accustomed conditions, and would not be productive of fundamental changes in the order of nature.
Being, like Mercury, nearer to the sun than the earth is, Venus also is visible to us only in the morning or the evening sky. ”

“ In short, all observers of Venus agree in thinking that her atmosphere, to a greater or less extent, serves as a mask to conceal her real features, and the possibilities of so extensive an atmosphere with reference to an adjustment of the peculiar conditions of the planet to the requirements of life upon it, are almost unlimited. If we could accurately analyze that atmosphere we would have a basis for more exact conclusions concerning Venus's habitability. ”

“ In those eight years the earth has gone round eight times, and has, therefore, regained its original position, while in the same period Venus has accomplished thirteen complete revolutions, and, therefore, this planet also has reached the same spot where it was at first. Venus and the earth, of course, attract each other, and in consequence of these mutual attractions the earth is swayed from the elliptic track which it would otherwise pursue. ”