THE PLANET VENUS.—Camille Flammarion
Revolving round the sun in 224 days, Venus has its motion combined with ours in such a manner that it passes its inferior conjunction, between the sun and us, every 584 days; but the plane in which it revolves is inclined 3° 23′ to that in which the earth itself moves. When Venus attains its greatest elongations from the sun it shines in the west in the evening, then in the morning in the east, with a splendid brightness which eclipses that of all the stars. It is, without comparison, the most magnificent star of our sky. Its light is so vivid that it casts a shadow. Sometimes, even, it pierces the azure of the sky, in spite of the presence of the sun above the horizon, and shines in full daylight.
The maximum visibility of Venus is produced by its greatest phase, by its greatest elongation from the sun, and by the clearness of our atmosphere.
The brilliant Venus was certainly the first planet noticed by the ancients, as much on account of its brightness as its rapid motion. Hardly is the sun set than it sparkles in the twilight; from evening to evening it removes further from the west and increases in brightness; during several months it reigns sovereign of the skies, then plunges into the solar fires and disappears. It was pre-eminently the star of the evening, the shepherd’s star, the star of sweet confidences. It was the first of celestial beauties, and the names conferred upon it correspond to the direct impression which it produced on contemplative minds. Homer called it “Callistos,” the Beautiful; Cicero named it Vesper, the evening star, and Lucifer, the morning star, a name likewise given in the Bible and the ancient mythologies to the chief of the celestial army.
The most ancient astronomical observation we have of Venus is a Babylonian record of the year 685 B. C. It is written on a brick and preserved in the British Museum.
The best hours for examining Venus in a telescope are those of daylight. In the night the irradiation produced by the brilliant light of this beautiful planet prevents us from distinguishing clearly the outlines of its phases.
When Venus occupies the region of its orbit behind the sun, with reference to us—which is called the point of superior conjunction—it is at its greatest distance, and is reduced to a disk of 9½ seconds in diameter. It comes imperceptibly toward us, and when it passes its quadrature, at its mean distance, it presents the aspect of a half-moon. It soon attains its most brilliant light, at the epoch when it shines at a distance of 39° from the sun, and shows the third phase 69 days before its inferior conjunction. Its apparent diameter is then 40 seconds, and the width of its illuminated part is scarcely 10 seconds. In this position we see the fourth of the disk illuminated; but this quarter emits more light than the more complete phases. Finally, when it reaches the region of its orbit nearest to the earth, it shows us nothing more than an excessively thin crescent, since it is then between the sun and us, and presents to us, so to say, its dark hemisphere. This is the position where its apparent size is greatest, and it then measures 62 seconds in diameter. After passing its inferior conjunction the phases are reproduced, in inverse order, as a morning star.
Venus is constantly visible in full daylight in astronomical instruments, even at the moment of its superior conjunction. It is then round and quite small. At the epochs of its inferior conjunction it presents itself under the form of a very thin crescent.
We sometimes notice that the interior of the crescent of Venus, the remainder of the disk, is less black than the background of the sky. This has been called the ashy light (lumière cendrée) of Venus, although it has no satellite to produce it. It seems to me that this visibility, rather subjective than objective, arises from clouds on the planet, which whiten its disk and vaguely reflect the stellar light scattered through space. The eye instinctively continues the outline of the crescent, and imagines, rather than sees, the rest.
The revolution of Venus round the sun is performed in an orbit almost exactly circular, and without perceptible eccentricity (0.0068), in a period of 224 days, 16 hours, 49 minutes, 8 seconds.
The days of Venus, also, are a little more rapid than ours, but not much. Since the year 1666 attentive observation of the planet led Cassini to conclude that it turns on itself in 23 hours, 15 minutes. This observation is extremely difficult, on account of the brightness of the planet and the faintness of the irregularities visible on its disk.
The year of Venus, composed of 224 terrestrial days, consequently contains 231 of its own, since the day is a little shorter there than here.
These same observations show that the axis of rotation of this planet is much more inclined than ours, and that this inclination is 55 degrees. It follows that the seasons, although each lasting but 56 terrestrial days, or 58 Venusian days, are much more intense on this world than on ours. They pass, without transition, from summer to winter.
The inclination of the world of Venus being more than twice as great as ours, we have only to take a terrestrial globe and incline it by the same quantity to understand the climates and seasons which will result. We may easily see that the torrid zone extends, in this case, up to the frigid zone, and even beyond it; and, reciprocally, the frigid zone extends to the torrid zone, and even encroaches on it; so that no place remains for a temperate zone. There is not, then, on Venus any temperate climate, but all latitudes are both tropical and arctic.
It follows, then, from all these circumstances, that the seasons and climates are much more violent and more varied than ours. This neighboring world shows nearly the same dimensions as ours. Thus this planet is truly the twin sister of ours.
The resemblance will be still more complete if we add that this world is certainly surrounded by an atmosphere.
When we examine with the spectroscope the light reflected by this planet we first find the lines of the solar spectrum (and this is natural, since the planets have no light of their own, and merely reflect that of the sun); but we notice besides several absorption lines similar to those which the terrestrial atmosphere gives, and particularly those of clouds and water vapor.
We may also add that attentive observation of the indentations visible on the crescent of Venus has shown that the surface of this planet is quite as uneven as that of the earth, and even more so; that there are there Andes, Cordilleras, Alps, and Pyrenees, and that the most elevated summits attain a height of 44,000 metres (27 miles). It has even been ascertained that the Northern Hemisphere is more mountainous than the Southern.
Even the study of the geography of Venus has already been commenced. But it is extremely difficult to draw, and the hours of sufficiently pure atmosphere and possible observation are very rare. This difficulty will be easily understood if we reflect that it is exactly when Venus arrives at its nearest to us that it is least visible, since, its illuminated hemisphere being always turned toward the sun, it is its dark hemisphere which is presented to us. The nearer it approaches us, the narrower the crescent becomes. Add to this its vivid light and its clouds, and you may imagine what difficulty astronomers have in dealing with it.
Twelve Views of Jupiter
Taken at Intervals within Six Consecutive Weeks
However, by observing it in the daytime to avoid the glare, and not waiting till the crescent becomes too thin, by choosing the quadratures, and making use of moments of great atmospherical purity, observers succeed, from time to time, in perceiving grayish spots, which may indicate the place of its seas.
Of what nature are the inhabitants of Venus? Do they resemble us in physical form? Are they endowed with an intelligence analogous to ours? Do they pass their life in pleasure, as Bernardin de St. Pierre said, or, rather, are they so tormented by the inclemency of their seasons that they have no delicate perception, and are incapable of any scientific or artistic attention? These are interesting questions, to which we have no reply. All that we can say is, that organized life on Venus must be little different from terrestrial life, and that this world is one of those which resembles ours most. The imaginary travelers to these worlds of the sky have always carried with them their terrestrial ideas. The only scientific conclusion which we can draw from astronomical observation is that this world differs little from ours in volume, in weight, in density, and in the duration of its days and nights; that it differs a little more in the rapidity of its years, the intensity of its climates and seasons, the extent of its atmosphere, and its greater proximity to the sun. It should, then, be inhabited by vegetable, animal, and human races but little different from those which people our planet. As to imagining it desert or sterile, this is a hypothesis which could not arise in the brain of any naturalist. The action of the divine sun must be there, as in Mercury, still more fertile than his terrestrial work, already so wonderful. We may add that Venus and Mercury, having been formed after the earth, are relatively younger than our planet.
The inhabitants of Venus see us shining in their sky like a magnificent star of the first magnitude, soaring in the zodiac, and showing motions similar to those which the planet Mars presents to us; but instead of showing a reddish brightness, the earth shines in the sky as a bluish light. It is from Venus that we are most luminous. The inhabitants of Venus with the naked eye see our moon shining beside the earth and revolving round it in twenty-seven days. They form a magnificent couple. Our planet seen from there measures 65″, and the moon nearly 18″; the moon seen from Venus shows the same diameter as the earth seen from the sun. Mercury is brilliant, and comes immediately after the earth in brightness. Mars, Jupiter, and Saturn are also visible as from here, but a little less luminous. The constellations of the whole sky show exactly the same aspect as seen from the earth.