Of all the planets lovely Venus is the one that is best known and most admired. It far exceeds all the other planets in brilliancy and beauty when as an evening star it hangs in gracious silvery softness above the sun, which has just passed below the horizon; and it is not less surpassing in loveliness when as a morning star it comes into view shortly before the sun rises, its glowing face still silvery and bright, but yet tinged with the rosy flush of the eastern morning sky.

In either position it never twinkles as Mercury sometimes does, but shines so steadily and softly that at times its disc can almost be seen with the naked eye, and it has such brilliancy that its light can often be seen in the daytime, if one knows when and how to look for the planet. At its brightest it frequently throws a light sufficiently strong to cast a shadow, as one may easily prove by holding a book or some other opaque object between Venus and a white background, such as the wall of a white house. It is six times as bright as the brightest of all the fixed stars, Sirius, the beautiful dog-star, which we see in winter chasing across the southern skies after Orion.

Venus’s superior brilliancy is due in part to the fact that it comes nearer to the earth than any other planet; but it is also intrinsically brighter than any of the others. From equal areas it reflects almost four times as much light as Mercury and three times as much as Mars.

WHEN AND WHERE TO SEE VENUS

When Venus appears in the sky she is not often mistaken for any other planet. Among all the planets she is the most readily recognized and the easiest to find. This is due largely to her extreme brilliancy and a peculiar silvery appearance that none of the other planets have; but also, in part, to her limited range in the sky, and her favorable situation for observation. Unlike Mercury, she is far enough away from the sun to be seen above the horizon for as much as three hours after sunset, and is then sufficiently high in the heavens to be seen free from the vapors of the atmosphere at the horizon. Yet, being one of the inferior planets, with her orbit smaller and nearer the sun than that of the earth, she can never get so far from the sun as to be at any uncomfortable height for viewing, and hence, when she can be seen at all, is always an obvious bit of brilliancy and a joy to the beholder. She is never higher in the sky than forty-five degrees, which is half-way between the horizon and the zenith, and is never farther away from the sun than forty-eight degrees. One frequently sees a bright planet higher up in the heavens than this; but it is never Venus nor Mercury.

We first begin to notice Venus in the evening sky about six weeks after she has passed superior conjunction. She is then very near the sun, and sets a little less than half an hour after sundown. Evening by evening she grows gradually brighter, mounts higher and higher in the sky and, consequently, sets correspondingly later, until in a little more than seven months after superior conjunction, and about six months after we have begun to watch her, she reaches her greatest elongation east from the sun. At that time she is usually somewhere near forty-five degrees above the sun, and is a very lovely and conspicuous object in the evening sky, setting a little more than three hours after sundown.

From this point she begins to travel back toward the sun, still becoming brighter each evening, because she is really coming nearer to us; and in about four or five weeks she attains the greatest brilliancy that she will have as an evening star during the particular revolution she is making. About twelve days after her brightest she will reach the point where she seems to be stationary for a time. This is when she is about to overtake us in our journey around the sun. After a short pause she will move on gradually, her course among the stars then being retrograde or westward; but what we most notice is that she is drawing nearer to the sun, setting earlier each evening, and becoming more and more difficult to see. At the end of about three weeks she is in inferior conjunction, on a line between us and the sun, and invisible. She has run her course as an evening star for nine and a half months, and has been visible anywhere from seven to eight months, the time of her invisibility depending upon the eye of the observer and the conditions of situation and atmosphere.

A week or two later we shall find her a splendid morning star, rising nearly an hour earlier than the sun. About three weeks thereafter she will be at her brightest as a morning star, and will continue to be very brilliant for some weeks. In about five more weeks she will have reached her greatest elongation west of the sun, and will rise about three hours and a half before dawn. Then she will begin to retrace her path, moving eastward, growing smaller all the time as she goes farther away from us, and showing a slower apparent movement, which gives one an agreeable sense of a reluctant parting, until after a little more than seven months she will have reached the sun and will again be in superior conjunction. She has then been a morning star for nine and a half months, and has been visible for about the same length of time that she was when she shone as an evening star.

This is a brief outline of a typical journey of Venus through one synodic revolution. She began one of these journeys on July 5, 1912, being then in superior conjunction. During the autumn of this year and the winter of 1912–13 she may be seen shining with great brilliancy in the west at sunset, and a few hours thereafter. Early in November, 1912, she and Jupiter will both be in Scorpio, where they will approach within two degrees of each other; and there is no doubt that their presence will add much charm to that region of the sky during the entire autumn.

About the middle of February, 1913, Venus will appear half-way up to the zenith at sunset. She will then be at her greatest distance east of the sun, and will be very bright; but, though a little nearer the sun, she will be still brighter shortly after the middle of March. A month later she will be invisible, and inferior conjunction will occur on April 24th. During most of May and all of June and July she will be a morning star, and her brilliant beauty will well repay an early morning outlook. She will get back to superior conjunction on February 11, 1914, and in that year she will be in an ideal situation for us to cultivate a more intimate acquaintance with her. From the latter part of March to November, 1914, she will be the brightest star in the western evening sky, and will do much to enhance the beauty of the pleasant summer evenings of that year. The sturdy, red-faced Mars will meet her on August 5th, a little more than a month before greatest eastern elongation, and might almost kiss her pale cheek as they pass within one-sixth of a degree of each other, a distance equal to less than one-third of the diameter of the moon.

The next long period when Venus will shine as an evening star will comprise the spring and early summer of 1916. She will be at her greatest distance from the sun during the last week of April, and will not pass from view until about the first of July. Then again she will be an evening star, and so seen in the west during the autumn of 1917 and the winter of 1917–18, reaching greatest eastern elongation during the first few days of December, 1917. Her next return to the evening sky will be for the first eight months of 1919, and the next will be for the winter of 1920–21 and the spring of 1921.

The synodic period of Venus is nearly five hundred and eighty-four days, or a little more than one year and seven months. That is, the planet returns to the same position with relation to the sun and the earth at intervals of about that length. The intervals do vary, however, as much as a week or more, owing to the various motions and situations of the planet and the earth. But every eight years Venus and the earth come around to almost exactly the same relative position with each other and the sun and the stars, and thus the appearances of Venus at the various seasons practically repeat themselves every eight years. The full splendor that she is to offer us in the summer of 1914 will be repeated in 1922, just as that of 1914 will but repeat that which she showed in 1906. And in each of the intervening years she will have again the same appearances that she had eight years before.

With the following table as a guide, the appearances of Venus can be followed through a number of years with sufficient accuracy for any but a close student of her movements. The exact dates of elongations and conjunctions will vary a few days, but for at least two or three multiples of eight years not enough to make any material difference in her various aspects.

The meetings of Venus with the other planets do not, however, occur with this delightful regularity. They all are moving about in their own ways, and engaged in their own affairs, and only the earth gets back to repeat the meeting with her in just eight years. These eight-year cycles are due to the fact that Venus makes thirteen revolutions around the sun while the earth makes eight. Her journey around the sun requires a little less than two hundred and twenty-five days (224.70), and the earth completes its revolution in a little more than three hundred and sixty-five days (365.25). So at the end of about two thousand nine hundred and twenty-two days—which equals eight years—they come into almost exactly the same relative positions in their orbits with which they started out, and begin the cycle anew.

DISTANCE AND BRILLIANCY

The mean distance of Venus from the sun is 67,269,000 miles. Her orbit more nearly approaches the form of a circle than that of any other planet. It is, like the orbits of the other planets, an ellipse, but of such small eccentricity that the difference between her greatest and least distance from the sun is scarcely more than a million miles. Light, traveling as it does, at the rate of a little more than one hundred and eighty-six thousand miles a second, goes from the sun to Venus in about six minutes. It takes something more than eight minutes for light-rays to come from the sun to us. When Venus is nearest the earth, her silvery beams come swiftly across to us in a little more than two minutes. When she is farthest from us, the rays of light require a few seconds more than fourteen minutes to travel over the distance. She is, when at her greatest distance, more than one hundred and thirty-five million miles farther from us than when at her nearest. This difference is due not to any great eccentricity in her orbit, or in that of the earth, such as causes Mercury’s great variations of distance, but to the situation of the two bodies in their orbits: they are nearest together when they are on the same side of the sun, and farthest apart when on opposite sides.

Usually at inferior conjunction Venus is a little more than twenty-five million miles from the earth. At her nearest possible approach to us, however, which takes place at inferior conjunction, when the earth is nearest the sun and Venus is farthest from it, a situation which occurs only once or twice in a century, the distance between us and the planet is only a little more than twenty-three million miles. This is nearer than any other heavenly body ever approaches us, except the moon and, so far as we now know, one small asteroid. Also, it is nearer than Venus comes to any other heavenly body except perhaps Mercury. Her nearest approach to that planet is also about twenty-three million miles.

Unfortunately, our comparative proximity to this beautiful planet does not much aid us in learning anything about her personal peculiarities. Shining only by reflected light, and being, like Mercury, situated nearer to the sun than the earth is, when she comes around to the same side of the sun on which we are, her unillumined side is turned toward us, and at the point of very closest approach she is absolutely invisible to the naked eye. Through a telescope, however, she can be seen up to the very point of inferior conjunction. What we see then is a mere curved line of light, so thin is the crescent she presents; but it is always apparent except when the planet makes a transit. During a transit she is actually in our line of sight with the bright disc of the sun, and is neither above nor below it, as at the ordinary times of inferior conjunction. The slender crescent that we ordinarily see offers a very narrow field for observation.

If there is any one on Venus who is studying the earth, he has a much easier task than we have in our effort to learn something about her. The earth is not only somewhat larger than the planet, but when the two bodies are nearest together the disc of the earth is fully illuminated, and so must show a splendid face; and then, our atmosphere probably interferes less with close observation than that of Venus. This little terrestrial system would undoubtedly shine as a magnificent pair of stars if observed from Venus. At that distance our moon would appear considerably larger than Venus appears to us when at superior conjunction, the earth would seem much larger than Venus ever does to us, and the distance between them would seem to be a little more than the apparent diameter of the full moon as we see it. The light of the earth must cause much more of a shadow than we ever get from the light of Venus.

It has been suggested that light from the earth is responsible for a dusky illumination of the dark side of Venus, which is occasionally seen, and which enables us to distinguish her entire outline even when only the merest line of a crescent is really illuminated. It is known to be earth-shine that causes what is apparently the same phenomenon often seen by us on the moon; but it seems that there is no reason to think that our earth, at its distance, would be sufficiently brilliant to illuminate Venus even so slightly. The cause of the illumination is not known; but it is thought that it may have some electrical origin, probably similar to that of our aurora.

Venus has the same phases that Mercury has. She shows her full face when at superior conjunction, and is then farthest away and smallest to our view. As she moves toward us she first becomes gibbous, and then, at eastern elongation, like a half-moon. 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. They were not known, however, until they were discovered by Galileo after the invention of the telescope in 1610.

Venus would be many times brighter than she ever appears if the entire disc of the planet could be seen when it is nearest to us. The apparent diameter of the disc at that time is nearly seven times larger than when we see it at the planet’s greatest distance from us. When Venus is in superior conjunction and farthest from the earth the disc measures only ten seconds, while at inferior conjunction its measure is nearly sixty-seven seconds. The diameter of the moon is about 1,868 seconds, so one could string across the diameter of the moon one hundred and eighty-six such planets as Venus appears to be when at her smallest, and only twenty-seven of the size that she appears to be when at her largest. Between these two extremes of size she changes gradually, day by day, from large to small and small to large, in ceaseless succession, as she approaches the earth and recedes from it in her orbital journey. Apparent diameter is determined by an actual measurement of the disc of a planet, and in the case of Venus indicates nothing as to brightness. When the apparent diameter is largest she is not visible to the naked eye.

VENUS’S LIKENESS TO THE EARTH

The fact that of all the planets Venus most resembles this good little earth on which our present lot is cast gives us a strong feeling of kinship with her, and a more lively interest in all her affairs than we might otherwise have. She and the earth are so nearly of one size that they are often referred to as twin sisters. There is a difference of less than three hundred miles in their diameters, the earth’s diameter measuring 7,917 miles, and that of Venus 7,629 miles. The surface of the planet is about ninety-three per cent. as extensive as that of the earth; its mass is a little more than eighty per cent., and its volume about ninety per cent. as great as the earth’s. Differing so little in these particulars, it follows that it must differ very little in density and gravity. The earth is the densest of all the planets, and Venus is only one-tenth less dense than the earth. Its force of gravity is not quite nine-tenths that of the earth. A removal from the earth to Venus would make just a comfortable reduction in one’s weight. A person weighing one hundred and seventy-five pounds here would weigh on Venus one hundred and fifty-four. If through strength of appetite and weakness of will one should take on two hundred pounds of too, too solid flesh here, transportation to Venus would bring about an instantaneous reduction to a solid one hundred and seventy-six pounds—as much of a reduction as would be compatible with health.

Venus must have begun her career in much the same way that the earth began its career. The nebula that formed her nucleus was probably nearly the same size (contained about the same amount of matter) as that with which the earth began its existence. The two bodies have succeeded in capturing about the same amount of loose material, and their gravity is such that they can hold within their bounds particles traveling at about the same rate of speed. No molecule of gas coming within the range of Venus’s attraction and traveling more slowly than six and thirty-seven hundredths miles per second can escape from Venus, and the earth can hold only such as move, when coming within its own attraction, with a less speed than six and ninety-five one-hundredths miles per second.

The earth has a moon, and Venus has none; but that may be because, like Mercury, Venus is too near the sun to be permitted to retain such a luxury. It is likely that if, in her earlier history, she had within the limit of her gravitative attraction the nucleus of a satellite, it would have been taken away from her by the stronger attraction of the sun. The same thing would have happened to us if we had been a little nearer the sun. And yet in 1645 a moon belonging to Venus was supposed to have been discovered, and it was thought to have been seen three times within the rest of that century, and four times within the first half of the following century. The last supposed view of it was in 1791; it has never been seen since. There is little doubt that it was an illusion of some kind. Perhaps, though, Venus has not the same need of a moon that we have.

ATMOSPHERE, DAY AND NIGHT, AND SEASONS

There is no doubt that Venus is in much better plight than Mercury, the other inferior planet, in regard to atmosphere. Until recently no one has questioned the belief that her atmosphere is very extensive—twice as heavy, perhaps, as that of the earth, dense, and full of clouds. The luminous ring about her, shown when she is making a transit across the face of the sun, points to a heavy atmosphere; and no less certain indications of it are given in the faint light which stretches beyond the termination of the horns when she is in the crescent phase, near inferior conjunction. Her very high reflecting power is also indicative of an atmosphere laden with clouds. White clouds form one of the most highly reflecting surfaces known, and the peculiar brilliancy of Venus is thought to be in great part due to the presence of large masses of clouds in her atmosphere. By the spectroscope, and in other ways, the water necessary to form clouds is shown to be abundant in her atmosphere. Even those astronomers who doubt the long-current belief in the large extent of her atmosphere concede an atmosphere of more or less density, though by one authority it is characterized as somewhat gauzy.

There is one vital point concerning the development of Venus upon which we have as yet no positive knowledge: the length of time in which she rotates on her axis. This is unfortunate, because until her time of rotation is known we cannot know much about her physical condition. Her rotation, we know, determines the length of her day and night, or whether, indeed, she has any. The time of it has been calculated to be anywhere from a little less than one of our days to two hundred and twenty-five, the latter being also the time of her revolution about the sun. Astronomers of equal reputation have come to exactly opposite results in their investigations. To one, the spectroscope has indicated the short day and night; to another it has shown no day and night, but a planet with one face forever toward the sun, like Mercury. What appeared to be stable surface markings have been observed, but have indicated under the eyes of different observers both the short day and no day at all. The disc has been measured during a transit, and shows so little flattening as to indicate a slow rotation and the long day. On the other hand, the best authorities think it unlikely that at the distance of Venus the sun could so retard the planet’s rotation as to make it coincide with its time of revolution. Thus the question is still an open one.

The truth may be that, owing to the density of her atmosphere, the surface of Venus has never been seen at all, and that the apparently stable markings are but clouds more or less lacking in stability. The difficulty of observing Venus will probably make it impossible to determine this point by visual observation. It may some day be settled beyond a doubt by the spectroscope. In some way it will surely be settled. Astronomers have too often made possible what seemed to be impossible for us to doubt that some one will find a way to discover this secret of Venus. With them a failure to prove a conclusion does not mean to abandon the subject, but to try some other means of getting at the truth.

The sun viewed from Venus would appear considerably larger than it does to us. Its apparent diameter to us is a little more than thirty-two minutes, while on Venus it would be something more than thirty-eight minutes; that is, it would appear about one-fifth larger on Venus than it does to us. This is enough to make a material difference between the two planets in the amount of heat and light they receive. Venus receives nearly twice (1.9) as much heat and light from the sun as we receive, but less than one-third as much as Mercury. If she had no atmospheric protection, there is no question but that she would have a climate disastrously warm for a race of beings constituted as we are. The normal temperature of an unprotected body at the distance of Venus is about 158° Fahrenheit (70° Centigrade).

If Venus is finally proved to have no alternations of day and night, she is still better off than Mercury, who has practically no atmosphere to protect him from the intense heat of the sun. How much protection she has depends altogether on the extent of her atmosphere. It is probably not enough to make the hot side comfortable from our point of view; and Venus, being undoubtedly a solid body with no internal heat, the cold side must be cold beyond anything we have any conception of. But there may be a very considerable part on each side that, owing to the refraction of light by the atmosphere, is more or less well lighted, and is also more or less protected by this same beneficent atmosphere from deadly extremes of heat and cold. In this situation there would undoubtedly be lively currents of air from the heated side to the cooler; but even these may in some way carry with them some tempering effects on the climate, as we know such currents do here on the earth.

If it should prove that the length of the day and night on Venus is something near that of the earth’s (and this seems not unlikely), she would then be indeed more like a twin sister to us. Being next to each other in our distances from the sun, and of nearly the same size, differing but little in density, mass, volume, and force of gravity, with her greater normal heat probably reduced by her heavier atmosphere to a temperature producing climatic conditions not very unlike ours, and with not very different alternations of day and night, we might well be considered more nearly related than any of the other members of the solar family.

The seasons, however, on Venus and the earth would not have much resemblance to each other. The axis of the earth is inclined to the ecliptic nearly twenty-three and one-half degrees, so that we receive the sun’s rays with varying degrees of obliquity during our yearly journeying around it, which is the cause of our agreeable change of seasons. Venus travels with her axis so slightly inclined to her orbit (a little more than three degrees) that each particular parallel of latitude receives practically the same amount of sunlight every day in the year, though at different parallels the sun’s rays strike with varying degrees of obliquity. However delightful or disagreeable the climate may be, there are no changes of seasons to speak of, and one could find variety only by going from place to place on the planet. She receives no compensation for this monotony by alternately receding from and approaching the sun as Mercury does, or by librations, such as he has. Her orbit being, as we have seen, so nearly circular as to permit of only small variations in her distance from the sun, and her axis so nearly perpendicular to her orbit, it follows that she has nothing to mark the year; and, whether she turns on her axis many times or only once during a revolution, life on Venus would be very monotonous to any one accustomed to our delightful variety of climate and seasons. Still, there is nothing in this monotony to prevent Venus from being a fairly comfortable habitation in some parts for such beings as inhabit the earth. The only real obstacle to habitability on Venus would be her lack of rotation and all that it involves.

Since we are not sure that we can see the surface of Venus, we cannot say what that surface is. Nevertheless, there is some reason to suspect that we would find there mountains of vast height. Certain irregularities have been observed at times, of a kind to indicate mountains covered with snow, extending beyond the clouds. They have been estimated to be many miles higher than any mountains we have on earth, their height depending somewhat upon the temperament of the observer. But inasmuch as these same high mountains have sometimes been thought to be only masses of clouds, it seems hardly safe to pronounce definitely upon them.

TRANSITS

On rare occasions, when Venus is in inferior conjunction, she makes a transit, and can then be seen as a black dot moving over the bright face of the sun. Transits can occur only when the earth and the planet are near the point where their orbits cross each other. The earth is at this point every year on June 7th and December 7th; but the orbit of Venus is such that she is there on the proper dates only four times in a period of two hundred and forty-three years. In every two hundred and forty-three years four transits take place. They occur in pairs, eight years apart, and in the same month. If a pair occur in June, it will be one hundred and five and one-half years after the last one of the pair until we have the first of the December pair of transits. After that it will be one hundred and twenty-one and a half years until we have the first of another pair of June transits.

The first transit of Venus that was scientifically observed was in December, 1639. It was the last of a December pair, there having been a transit eight years before, in December, 1631. One hundred and twenty-one and a half years later, in 1761, a June transit occurred, and in 1769 another one took place in June. Then there were no more for one hundred and five and one-half years, when we had a December pair in 1874 and 1882. The next ones will be in June, 2004 and 2012.

Great importance was attached to those transits that occurred in 1874 and 1882, because they were expected to be useful in determining with greater exactness the distance of the sun. Extensive preparations were made for scientific observation of them; but the results were not satisfactory, largely because the atmosphere of Venus prevented her from showing a sharp outline at the moment of entering upon and of leaving the face of the sun. The main scientific value of a transit of Venus now is in the opportunity it may offer to investigate the nature of her atmosphere. Even though that interesting question may have been practically settled before another transit takes place, it will be important to know to what degree the phenomena observed at the next transit confirm the decision.

On account of the surpassing brilliancy of Venus, the brightest of all the heavenly bodies after the sun and moon, she was to the ancients the most important of all the stars and planets. She was the supreme evening and morning star. As evening star she was known as Hesperus, or Vesper; as a morning star she was called Phosphorus, or Lucifer, and under all these names she is frequently mentioned in Greek and Latin and kindred literatures.

The symbol of Venus is ?, a figure which is nothing more than the conventionalized form of a looking-glass, an article that is often pictured in the hands of the goddess for whom our beautiful planet was named. In her general aspect she is as placidly splendid and charming as ever a goddess could be, and it is not strange that the happy ears that could hear such strains should find her, as they did, singing a rich contralto in the music of the spheres. Jupiter and Saturn, under this mythological apportionment, sang bass, Mars took care of the tenor strains, and the high soprano was carried by our little dwarf Mercury.

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