The planet that varies most in the beauty of its aspect is Mars. It is as much as fifty times brighter when it is nearest to us than it is at its greatest distance from us. At its brightest it is many times more brilliant than any of the first-magnitude stars; but when it leaves our neighborhood and goes far off into space in its journey around the sun, its glory is so dimmed that it becomes not brighter than an ordinary second-magnitude star, such as the pole-star, and less brilliant than the brightest stars in the Big Dipper. These extreme changes of brightness are due not so much to any great distance that Mars goes from us in comparison with other planets as to its coming so very near to us at times. It is, after all, a small body, and no great distance, as heavenly distances go, is required to make it show so. But the HOW TO IDENTIFY MARSBut with all his variations in brilliancy and beauty Mars remains ever a charming, rosy-hued planet, shining always with a steady, clear light, and when once we have come to know him is not easily mistaken for any other planet, or for any of the brilliant stars that may more or less resemble him in color. Red in varying degrees of intensity is, perhaps, the most obviously distinguishing mark of Mars; but his own characteristics are never more distinct than when his THE TWO PHASES OF MARS We see its full face when it is opposite the sun. When half-way between opposition and conjunction it becomes gibbous, as shown in the photograph on the right. These photographs were made at the Mt. Wilson Observatory. Mercury is the only planet that in color even suggests Mars, and for Mercury it can never be mistaken after one has once seen the two planets. Mercury, we know, is always very near the sun; but when visible at all is, even in that unfavorable situation, always as bright as a first-magnitude star. On seeing a planet, then, sufficiently high above the horizon to attract one’s attention, one may be sure that it is Mars if it is red, and equally sure that it is not Mars if it does not show this color. Under certain atmospheric conditions the sun, moon, and all the planets sometimes appear red when they are very near the horizon; but in this situation there is always something other than color that marks them. If its color is not a sufficient mark by which to identify Mars, a still further difference between it and the stars is its markedly rapid movement. A single night will make a sufficient change in its position to show the planet as a wanderer. On an average, it travels over about four-tenths of a degree in the heavens in one day. This equals more than half the diameter of the moon, a change of position sufficiently great to be easily detected. WHEN AND WHERE MARS MAY BE SEENUnlike Mercury and Venus, which are never far from the sun, and can be seen only for a comparatively short time either early in the morning or in the evening, and are never very high up in the skies, Mars may be situated so that it can be seen at any time of the night, and also at any distance from the sun. When it is in opposition it rises just as the sun sets, and is then in view all night. At this time it is nearer, larger, and brighter than at any other time in the particular revolution it is then making, and, consequently, is in the best position to be viewed by us that it will have during that revolution. Oppositions differ, however, in different revolutions, and some show us the planet more splendidly brilliant than it appears at others. The oppositions at which Mars shows most brilliant take place, fortunately, in the summer and early autumn—the seasons which are most agreeable for outdoor observation. He is then traveling through that region of the sky, sparse in stars, that lies between Sagittarius and Aries; and, since the ecliptic there runs rather low in the sky, These favorable oppositions occur in the summer because the earth is in line in the latter part of August with that point in the orbit of Mars where the planet makes its nearest approach to the sun. Oppositions never occur when Mars is exactly at that point; but they do occur when he is very near it, and at such times we see him in his greatest glory. This happens once every fifteen or seventeen years. But at any summer or early-autumn opposition Mars is not very far from this nearest point to the sun, so that at any oppositions during these seasons he is very brilliant and almost as bright as when he is at his best. The earth is in line in the winter with that part of Mars’s orbit which carries him farthest from the sun, and at opposition then he is much less bright than at the summer oppositions. He is at the same time in those constellations which pass nearly overhead in the sky, and cannot be quite so comfortably seen at all times in the night as he can be in the summer. The very best and most brilliant oppositions occur in the latter part of August or in the early part of It is worth one’s while, even at some inconvenience, to see Mars at whatever time he is in opposition, for he is a delight to the observer, and always notable in the part of the skies through which he is then passing. There are some aspects of the planet that are so charming at a winter opposition that it is a positive loss not to have seen him at such times. He is more isolated and conspicuous in the summer; but he fits well in that gay company of winter stars that shine more brilliantly than any others, and we can easily feel something akin to family pride as we watch him moving so graciously among them. Mars makes a complete circuit of the skies, and comes back into the same position with relation to the sun and the earth on an average every seven hundred and eighty days, For mere purposes of naked-eye observation the variations in the synodic period of Mars do not make any difference, for the planet is in view practically all night for many nights before and after opposition, with changes of brightness too small to be noticed by an untrained eye. For at least two months at the time of opposition it has almost the same aspect to us. At that time it is always in the east early in the evening, and shines all night. For nearly nine months afterward it is visible and conspicuous in the evening sky, appearing each evening nearer and nearer to the western horizon, until finally, in a little more than a year after opposition, it passes behind the sun and becomes a morning star. But, as it then rises before the sun and passes across the heavens in the daytime, it is invisible Mars will be in conjunction in November of this year (1912), and will not be visible in the evening during 1913 until toward the end of the year. The next opposition after the publication of this book will occur in January, 1914. From that time until the following autumn the planet may be seen in the evening. In 1915 Mars will not be visible in the evening sky until late in the year. After November it will be in the east in the evening, rising earlier each evening, until at opposition, early in 1916, it will rise at sunset and will be visible in the evening during the entire summer and autumn of that year, but will not be extraordinarily bright. In 1917 it will be again invisible in the evening. In 1918 it will be in opposition in the early spring, and will shine in the evening all the rest of that year. It In 1924 there will be an exceptionally brilliant opposition, which will occur during the last week of August, and the planet will then be about as brilliant as it ever appears, and will be very favorably situated for observation in the constellation Pisces. We shall then see Mars in the flame-like phase of his beauty, and he will dominate the evening sky during the whole of that summer. At oppositions such as this one Mars is more favorably situated for observation from the earth than any other heavenly body except the moon. The next oppositions will take place the last week in October, 1926, in December, During the years that Mars does not appear in the evening we need not be deprived of a sight of the planet if we will look for it in the morning sky. A few months after conjunction it may be seen as a morning star, rising shortly before the sun. It rises earlier each morning, and hence can be seen each morning for a longer time. After its hour of rising has reached midnight it then passes into the evening sky and rises earlier each evening until it reaches opposition. The movement of Mars among the stars, as we see it, is generally toward the east, and we can see by looking that it changes its place among the constellations in that direction, going from Aries to Taurus, from Taurus to Gemini, and so on. On each side of opposition, however, the planet appears for a few weeks to be moving westward among the stars. This is the retrograde motion which an outer planet appears to have when we are overtaking and passing SIZE, ATMOSPHERE, AND TEMPERATUREIn size Mars is one of the smallest members of our solar family. Its mass is a little more than one-ninth that of the earth, and its entire surface is only about one-third as great as ours. It is the merest trifle more dense than Mercury, but only about sixty-six one-hundredths as dense as the earth. Its force of gravity is about thirty-six one-hundredths as powerful as that of the earth. A man weighing two hundred pounds here would be relieved of about one hundred and twenty-four pounds of his weight if transported to Mars, weighing there only seventy-six pounds, which would greatly increase his efficiency if he were in other respects the same. It would necessarily follow that Mars, having such small force of gravity, could not long retain a heavy atmosphere, even if it had set out with such a one. No molecule of gas moving at a greater speed than three and thirteen-hundredths miles a second could be held by Mars in its atmosphere, and so The famous white polar caps, which furnish so many news items to the journals, are also of uncertain origin, and their true nature can be determined only by a fuller knowledge of the atmosphere of Mars. They appear in the winter season on the planet and disappear in its summer, so there seems to be no doubt that they are dependent in some way on the temperature in the polar regions of Mars. If they are hoar-frost or snow, they are condensations of water vapor; and, in that case, when they disappear there must be sufficient heat to melt them. It has been contended that the sun’s rays fall too obliquely on the poles of Mars to melt more than a few inches of snow, but that the caps may be light snow or frost, and thus capable of being dissolved by even such oblique rays of sunlight as they receive. Also it has been suggested that the deposit resembling snow may be carbon dioxide, which condenses into a white substance at a temperature more than a hundred degrees (-109° Fahr.) lower than is necessary to produce snow and melts at a correspondingly low temperature. What the nature of the phenomenon seen at the poles of Mars is depends largely upon what the tempera The normal temperature of an unprotected body at the distance of Mars from the sun is about thirty-two degrees blow zero (Fahrenheit); and since we know Mars has no dense atmosphere to retain the heat it acquires, it is natural to suppose the existence there of a very low temperature, and one incompatible with our ideas of life and growth. The most favorable conclusions do not place the mean temperature higher than forty-eight degrees Fahrenheit. It is certain that the planet must be subjected to great extremes of temperature within its range, since its filmy robe of atmosphere cannot protect it to any extent from the direct rays of the sun during the day, nor prevent the heat from escaping with great rapidity at night; so that, whatever heat it may gain in the daytime, it probably loses much of it during the night. Until we know more of the constitution of the atmosphere of Mars we can know nothing certainly about its temperature beyond the fact that it is much colder than ours and more subject to varia DISTANCE AND BRILLIANCYMars is, on an average, about one and a half times farther from the sun than we are. Its mean distance is, in round numbers, one hundred and forty-one million miles; but, since its orbit is very eccentric—more eccentric than that of any other of the planets except Mercury—its distance from the sun varies as much as twenty-six million miles. At its nearest the planet is a little more than one hundred and twenty-eight million miles from the sun. Its greatest distance from that luminary is one hundred and fifty-four million miles. At its mean distance something more than twelve and a half minutes are required for light to travel from the sun to the planet. The sun becomes quite a medium-sized object as viewed from Mars, and must lose some of the majesty of aspect that it has to us. Its apparent diameter is about twenty-one minutes, which would make it less than two-thirds as large as we see it. The average amount of light and heat that it furnishes to that poor, lightly clad little planet is less than half as much as we receive, though when the planet is at perihelion the sun’s radiance is forty per cent. more powerful than when it is at its greatest distance from the source of these life-giving forces. The eccentricity of the orbit of Mars is the cause also of his great variations in distance from us, and hence of his extreme changes in brilliancy. These changes are many times greater with reference to the earth than to the sun. At the planet’s nearest approach to us it comes a little nearer than thirty-five millions of miles. This is when it is in opposition in August. When opposition occurs in February, it is as much as sixty-two millions of miles from us; and when it is in conjunction, and on the other side of the sun from us, it is sometimes two hundred and forty-eight million miles dis While Mars does not exhibit the phases of the inner planets Venus and Mercury, by showing a disc sometimes at half-full and sometimes at crescent it is sufficiently near us to be, in certain positions, gibbous, or to show a little less than a full face. When this occurs Mars is about half-way between opposition and conjunction, and the earth and the sun are so situated that we are slightly to one side of the fully illuminated face of Mars. This phase, however, is not sufficiently marked to make any material difference in the brilliancy of the planet. It is not apparent without the aid of a telescope. From Mars the earth shows all the phases that Venus shows to us. When Mars is flaming down upon us in his position of greatest brilliancy we present to him a thin MARS: DIFFERENCE IN ITS APPARENT SIZE AT ITS NEAREST, MIDDLE, AND FARTHEST DISTANCE FROM THE EARTH Mars appears fifty times brighter when nearest than when farthest away. DAY AND NIGHT, AND SEASONSOwing to the undoubted permanent markings on the surface of Mars, astronomers have been able to determine the length of its day with much less likelihood of error than in the case of any other planet except the one on which we dwell. It rotates on its axis in twenty-four hours, thirty-seven minutes, and twenty-three seconds, which makes its day nearly forty minutes longer than ours. In our greed for all too fleeting time we may feel a little envy of these extra minutes, which would mean so much to us if added to our day. But they do not seem so important when we consider that while Mars is having six hundred and seventy of these days we are having six hundred and eighty-seven of ours, which, after all, seems to give us eighteen days more of time. Our attitude toward the situation depends upon the point of view. The axis of Mars is inclined to its orbit SURFACE ASPECTS OF MARSSeen through a telescope, Mars is not so red as it appears to the naked eye. One of the best observers of it has compared it to an opal, and it surely has some of the qualities of an opal in the diversity of aspect that it shows to different observers from different points of view. No other planet has been so subjected to controversy over what appears on its surface. This is partly due to its being the only planet whose surface is without doubt open to our view and in a situation where it can be minutely studied, and partly to the fact that the controversy involves questions concerning life and intelligence, which are always of intense human interest. Matters of this vital sort are never accepted without dispute. That is one way of getting There are recorded observations made of Mars as early as 272B.C., more than two thousand years ago, and it has been nearly two hundred and fifty years since the snow-caps were first seen. Through the telescope not only the snow-caps are plainly visible at the proper seasons, but there are also visible dark patches over the surface, showing a variety of color, and in certain parts changing somewhat as the seasons change. It is one of these patches, the outline of which suggests a somewhat twisted eye, that is known as the “eye of Mars.” The main surface of the planet is reddish yellow in color; the patches on it are variously described as gray, grayish green, or blue, colors which in combination could easily take on a tone of any of them according to the eye of the observer, and this portion of the planet’s sur When the planet’s differences of color were first observed, the reddish-yellow portion was supposed to be land, and the areas of varying bluish-green and gray were thought to be the waters of the ever-changing seas. A little after the middle of the last century some keen eyes saw a few streaks or markings of some sort across the land areas, and in 1877 a close study of the planet by an eminent Italian astronomer, Schiaparelli, brought to his view many greenish streaks, all directed toward the so-called seas, and sometimes seeming to intersect there. In publishing this discovery Schiaparelli called these streaks canalli, which is properly translated “channels,” but appeared in English as “canals.” Since “canal” with us means artificially constructed waterways, the discovery became at once one of universal interest; for artificial waterways mean human beings to construct them, and it was an intensely interesting thing to know that Mars was probably inhabited with beings at least somewhat after our own kind. It was a new world. The little planet became a topic of absorbing interest to all of us. And thus began the In our own country the observatory at Flagstaff is the one the best known among those doing research work on Mars; but it is not the only one. The observatory there is finely situated in the thin, clear atmosphere of Arizona, the mechanical facilities for such work are good, and there seems no doubt that there are there some observers who have eyes that were made for seeing. All that the sharp vision of Schiaparelli saw has been seen there, and much more. Several hundred canals have been discovered, and at certain seasons many of them have appeared to become double. Their courses have been followed, and their appearances Naturally, when a person has discovered any new and curious phenomenon in nature he seeks to determine the exact meaning of it. It would have very little interest for him if he did not, and it would be a dry lot of facts that did not arouse a desire to do this. The interpretation put upon what has been seen at the observatory at Flagstaff is, in brief, about as follows: The surface of Mars has no oceans or mountains. The reddish areas, which form the larger part of the surface, are deserts. The blue-green streaks are ribbons of vegetation along each side of artificially constructed waterways, which are of immense length and cross and recross each other until they somewhat resemble a network of lines over the desert surface of the planet, These conclusions concerning what is seen on Mars are not held by any one to be completely proved, but are thought by their author to follow reasonably from the phenomena as observed. By persons of a different temperament they are regarded as too complete an explanation, particularly as the data upon which they are founded are not undisputed. Some of the best astronomers have not been able even to see the multitude Also, it is not at all certain that there is sufficient water vapor in the slight atmosphere of Mars to furnish the snow necessary for this great irrigating system, nor the heat to melt it at the proper season. The natural temperature of Mars would be, as we have seen, very low, and unless it is modified in some way not yet indicated everything points to a frigidity too intense to permit the continuance of life and growth of any sort known to us. These things must all be reckoned with before anything certain can be known of the surface of Mars. The difficulty of pronouncing upon the minute details is impressively indicated by Professor Moulton, who says that, even under the finest conditions and with the best telescopes, it is like view The mere fact that some astronomers have not seen the lines on Mars does not mean that they deny their existence. Some eyes have greater defining power than others, as well as some telescopes, as every one knows. But while all the lines and patches of color that are claimed to have been seen on Mars doubtless have been seen by some persons, yet it is not necessary to accept the interpretation of them given by lively-minded observers when it is not convincing. There may be vegetation on Mars, and even intelligent beings. We do not know; and thus far there is not much to support, even by inference, the view that there are. If we want the truth, we are brought no nearer to it by giving full credence to a speculative theory simply because it is interesting and pleasant; and thus far all theories advanced as to the nature of the surface markings on Mars are speculations, though there is no doubt that THE SATELLITES OF MARSMars has a little family of two moons. Tiny little bodies they are, the smallest in the solar family except, perhaps, an occasional asteroid. Neither one of them is more than ten miles in diameter, and the two together are smaller than any other known satellite. They can only be seen when Mars is in opposition, and then only with a fairly large telescope. They were discovered in 1877, and named Phobos and Deimos, the names of the two attendants of the god of war. Phobos is the brighter and the nearer to the planet. It is less than four thousand miles from the surface of Mars; and on account of its being so near and the shape of Mars being a spheroid, like that of the earth, the little satellite can never be seen from Deimos is not any larger than Phobos, and not as bright; but it is slightly less difficult for us to see, because it is between two and three times farther away from Mars than Phobos is, and thus not so much lost in the light of the planet. It circles around Mars in a little more than thirty hours, and this, being only six hours more than Mars consumes in turning around on its axis, results in requiring more than two days for the satellite to pass from rising to setting. Between rising and setting it goes through its phases four times. It can be seen from The symbol of Mars is ?, a conventionalized figure representing a shield and a spear—implements of war appropriate for the use of the deity especially connected with warfare. |