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Companions of the Sun—I

Some of the More Intimate Features of the Solar System

LIMITED to a narrow physical environment we have developed what may be termed a physical consciousness. Even the blaze of the stars, that jewels night with a serene beauty challenging word pictures in vain, deceives us with a nearness which is only apparent. The earth seems solid enough and even the heavens appear to be within reach. A child thinks that with a long ladder, he might climb up into the sky and shovel the snow down. We are all near children, and it is hard for any of us to realize with one of the oldest writers of the race that “ He stretcheth out the north over the empty place and hangeth the earth upon nothing.” Yet the solid earth which serves us for a foundation has itself nothing solid on which to rest, but like all the other companions of the sun, is suspended in space by cables of law. If our earth-mother did not hold us closely to her bosom we should ourselves fly out of her arms and become prodigals like many another piece of free and independent world-stuff. We cannot see the solar system whole. Being a part of it ourselves; while we look at a second part, a third part is behind us. Those companions of the sun seen by us at any time are strewn over the wide ceiling of space and mixed with the stars. It is clear, therefore, that we can see the solar system only ideally. Finding oceans of- space on all sides of us, we are at first overawed by the sense of our utter insignificance. We seem almost lost in the universal immensity. Our thought is plunged into interminable deeps. Nevertheless, we too are composed of star-stuff, and are essential parts of the whole cosmos. Even a child may say from the vantage of the soul view: "The open heavens are too small to contain me, I contain them." Let us, then, try to see the solar system as clearly as if there were nothing else in the heavens, and we looking on it from the outside. The unwearied endeavors of countless investigators, toiling through nnumerable years, despite inconceivab1© difficulties and discouragements, enable us to get an z\,'x.'2zytz conception of what the solar system would look like if we could see it alone and see it whole. Imagine then, a great wheel of worlds with a hub more than six hundred times as large as the combined volume of all the orbs that encircled it. This sun-hub is brilliant, blazing, colossal. Jupiter with his nine moons or Saturn with his ten moons and his rings, is but a toy in compar'son with this almost inconceivable pageant. The zodiac is the rim of this vast wheel, and we of this little earth are in the plane known as the ecliptic plane, because here all the eclipses seen by us take place. Looking at this wheel from the outside, yet from the plane of the ecliptic, it would resemble a long line of orbs extending over 6,000 000,000 miles, with the sun blazing in the centre. The sun's diameter is about as one mile in seven thousand of the length of this line of sun-companions. This makes the sun seem comparatively small. Yet if our moon had a satellite revolving in the ecliptic plane at a distance of 190,000 miles, it would be possible for the earth to stand at the sun-centre and our moon could revolve around the earth, and the satellite of the moon could revolve around it, and all would still be far within the circumference of the sun. If our eye were placed above the plane of the ecliptic, we should see the solar system as an ellipse somewhat after the appearance of Saturn and his rings at the present time. As our eye rose higher above the ecliptic plane, the smaller diameter of this ellipse would increase till finally it would be a near circle. The companions of the sun comprise eight planets , twenty-seven moons, hundreds of comets, and thousands or even millions of meteors and tiny particles of world- stuff, all floating along with the great household of the sun. They may be classified as follows: The major planets and their moons. The minor planets. The comets and meteors. All these bodies are moving around their primaries in elliptical orbits. Of the eight major planets, the four nearest to the sun are much smaller than the others, indeed, they are as to their size, pretty well within the class of large moons. Mercury, Venus, and Mars are quite perceptibly phased to our vision, whereas the larger, outer four owing to their comparative distance from the sun, are free from any perceptible phasing. The two innermost planets, Mercury and Venus, are without moons, being exceptional in this respect; indeed, they may themselves almost be regarded as moons, since they turn always the same face sunwards. This coincidence of rotation with the revolution periods obtains in the case of all the moons where, in the nature of the conditions, such a coincidence is determinable. (See Bulletin No. 64, Lowell Observatory.) Journal of the rioyal Astronomical society of Canada. Note—the nunbers in this article, thouto only approximate, are reasonably a curate—A. D. W. The solar system is the unit of group astronomy. There are probably, in other solar systems than ours, bodies with characteristics not represented in our group, but on the whole, the system in which we live is a good example of the family of a star. The unit of distance within our sun-family is the distance of our earth from the sun, which is roughly 93,000,000 miles. It is known as a sun distance. Out in the general star-fields the unit of distance is the space covered in one year by a light- ray, and is called a light-year. This amounts to over five trillions of miles, or over 60,000 sun-distances. The star nearest us, so far as we have been able to ascertain, is Alpha Centauri at four and two-fifths light- years distance from us. Here, then, is our solar group or star family moving on in space at a rate of nearly 12 miles per second, its individual orbs all the while revolving, rotating, librat- ing, describing polar circles in the sky, and acting like a group of gyroscopes held together by chords of infinite harmony, and marching to the music of the morning stars. Mercury is three-eighths of a sun-distance from the solar centre, turns always the same face to the sun, and can be seen only when its line to the sun is nearly at right angles with ours. He is too bright to see in much detail. It has been stated that Copernicus never saw Mercury, but apart from its general improbability, there is evidence to the contrary.1 Mercury is the smallest of the major planets. (Diameter, 3,000 miles.) His orbit is inclined at an angle of seven degrees to the plane of the ecliptic, hence he passes between us and the sun only twelve times in a century whereas if it were coincident with that plane we should have a transit of Mercury at least three times a year2. Two pounds on the earth's surface would weigh but one in Mercury. His axis of rotation is nearly perpendicular to the plane of his orbit, which being very eccentric,' produces a season dependent upon his varying distance from the sun. His greatest removal from the sun varies to his least as three to two. Having no appreciable atmosphere, Mercury is not eligible as a health resort. His year consists of 88 of our days or less than three months. Dividing this year into summer and winter according to his less or greater distance from the sun, each of these periods of about six weeks measures a semi-revolution in his orbit. The coldest hour in winter on the sunward face of Mercury is probably hotter than the boiling point. The hottest hour on the anti-solar hemisphere must be comparatively cool and may have been the abode of intelligent beings before its atmosphere was exhausted. If there ever were such beings, they must have kept out of the sunlight. The strongest contrast of Mercury with all the other planets is in the fact that its orbital inclination to the ecliptic plane is three times as great as the average of all the other planets and more than double that of the next greatest which is Venus. Venus is the earth's nearest neighbor in the sun- family, being two-thirds of a sun-distance from the solar centre. She is about the same size as the earth, and in all probability keeps always the same face sunward. Her year is about seven of our months, and as her axis is perpendicular to the plane of her orbit, which is nearly circular, there are no seasons in Venus. She is a warm planet, but her dense atmosphere moderates the heat. If she turns always the same face to the sun, as appears increasingly probable, this fact bears an interesting relation to the question of the habitability of this planet. The sunward hemisphere would, in that case, be too hot for habitation, and it is possible that the opposite side would be too cold. There is a borderland, which we might name the twilight circle, out of the direct sunrays yet not entirely dependent upon starlight, where it is reasonable to suppose that habitation may be quit£ feasible. HDlmstead, in Letters on Astronomy, page 230, says: “ Copernicus . . . lamented on his deathbed, that he had never been able to obtain a sight of Mercury,” but Berry of Cambridge, in A Short History of Astronomy, page 96, says: Copernicus, moreover, points out in more than one place that the high latitude of Frauen- burg and the thickness of the air were so detrimental to good observation that, though he had occasionally been able to see the planet Mercury, he had never been able to observe it properly.” For a fuller discussion see this Journal, vol. 9, page 264, 1915. The next transit of Mercury occurs May 7th, 1924. Owing to the inclination of her orbit of three-and-a- half degrees to the ecliptic plane, Venus transits the sun only at intervals of eight and 122 years alternately. Venus is never seen from earth at midnight, as her elongation or distance from the sun east or west never exceeds 45 degrees. She is often seen by daylight, especially in an intensely blue sky when a cloud passes over the sun. It is very important to know exactly where to look, though some have seen it when not looking for it. Venus when brightest has about twelve times the brightness of the most brilliant fixed star. We have little likelihood of ever finding evidences of life on Venus, but the Venutians, if there be any, may find our planet a most interesting and easy object of telescopy. The relations in this respect are the reverse of those with the hypothetical Martians. As the face of the earth as presented to Venus is about four times as large as that which Mars presents to us, we may be sure that the people of Venus, with means of scrutinizing the heavens similar to ours, could see far more of our life than we could reasonably hope to see of Mars'. They would have excellent maps of the physical geography of our planet, showing continents, islands, oceans, rivers, mountains, etc. As Venus is a difficult object of observation to us, so also for similar reasons, the earth would be exceedingly difficult of observation from Mars. Unless clouds obstructed their view, the polar snow- caps of the earth would be readily visible from Venus. As the earth is sometimes 10,000,000 miles nearer to Venus than Mars ever is to us, and has four times the apparent surface presented, the only hindrance to results would be the possible conditions on the surface of Venus. Have they telescopes? Are their clouds too dense? Are there pet\ where at all? The phases of V .nus are most interesting, especially at the period just before her inferior conjunction, when she passes between the earth and the sun. She then has the outline of a new moon, and is most beautiful, appearing as a perfect silver bow. Six pounds on earth would weight five on Venus. The Earth is the third planet from the sun. Besides the three motions common to all planets, rotation, revolution, and progress with the sun, the earth has several other motions or librations due to lunar and near planetary attractions. The axis of the earth points at present to the vicinity of the pole star, but is describing a figure in the heavens which it completes in 25,800 years. The earth has also a magnetic period, and an auroral period, both of which appear to have definite relations with the sun-spot period of our solar centre.- Objects are lighter at the equator than at the poles. Time-recording pendulums have to be shortened for frigid latitudes. This is because the semi-diameter of the earth and also the centrifugal force are greater at the equator than at the poles. The atmosphere of the earth helps to diffuse the light and mitigate the blackness of the shadows cast by the earth at night. It shields us from the destructive power of meteors, protects us by radiation from extreme heat and cold, and hides the stars in the day time. The blue sky would be black were it not for the atmosphere. Besides these effects, there are many beautiful and interesting phenomena due to the atmosphere. Among these may be mentioned the earth's shadow thrown up as a dim arch in the eastern sky as the sun sinks behind the western horizon. It is seen as a wide-sweeping arch gradually rising in the east awhile after the sun has disappeared. This twilight shadow is much modified by the atmosphere. Another phenomenon dependent doubtless to a considerable extent upon the density or rarity of the atmosphere is the Aurora. While the frequency and, indeed, the final cause of aurorae are probably to be found inthe sun and those disturbances of solar energy related to the sun-spots, there seems to be a state of the atmosphere which is peculiarly suited to their display. 'In a letter from a friend, dated Muskoka, August 20th, 1909, at 12.18 p.-m., the following observation is reported: “About four minutes ago, I was watching a tiny cloud-craft sailing high in the east, far from any other clouds. I watched it till it was absorbed in the blue. Then, my eyes, dropping a little lower, beheld—Venus, yes, Venus, and the sun shining! I think there must have been a slight veil over the sun, for I looked away from Venus for about a minute, and when I looked back, I could not see her. The sky had become an intenser blue, and the sunshine seemed brighter. There are now some clouds floating in that part of the sky. I shall try to see her again before I go in to lunch. 12.41—Had quite a time finding her again. Watched her till a huge cloud that had partly obscured the sun covered her.” A. A. E. The Moon is the fifth in size among the satellites of our solar sj stem. Three of Jupiter's and one of Saturn's are larger, but ours is the largest of all in proportion to the mass of its primary. It follows the law governing the moons by turning always the same face towards the earth, but owing to a swinging motion, we see in all about four-seventh of its surface. On the moon there is no atmosphere to support life, no water and no weather. There is no sudden change of temperature in the constant sunlight. That portion of the sphere that receives no sunlight is partially illuminated (except at full moon) by earthshine. The remainder is so black that to go into the moon's night where it is not earth-illuminated is to disappear. As the orbit of the moon is inclined to that of the earth at an angle of five degrees, lunar eclipses which otherwise would occur once in every lunar month, are somewhat infrequent, occurring never more than three times a year. This is obviously when the sun, the moon, and the earth are all in the ecliptic plane, the moon being therefore at one of the nodes where it crosses the ecliptic. Solar eclipses also occur only when the moon is crossing the ecliptic, therefore at new moon as distinguished from lunar eclipses which occur always at full moon. Solar eclipses never occur less than twice nor more than five times a year. The mountains of the moon are much higher than our terrestrial peaks in proportion to the size of the orb. Accurate measurements are impossible because of the absence on the moon of a sea level from which to measure the heights of the mountains. All that can be done is to measure from the surrounding plane. The highest peak heretofore measured runs up 24,000 feet. The moon does not perceptibly affect the earth's weather, except to glorify it with a soft, silver light. Our moon is the most beautiful of all telescopic objects, and has been the comrade and conniver with poets and lovers in all ages. There is accumulating evidence that some of the lunar craters are not yet dead, but there is no animal life and no vegetation on the moon's surface. Six pounds on the earth would weight only about one on the moon. Mars. Mars is the most easily observable of -all the plants fror,; tue viewpoint of the t-«rth. We car see the snow-line advance and recede at the Martian poles as winter or summer prevails. His orbit is inclined to the ecliptic plane at an angle of 1° 51'. His axis leans to his orbital plane between 23° and 24°, this being almost the same as that of the earth. His axial inclination and h.'s orbital eccentricity, which is greater than other major planets excepting Mercury, accentuate his seasonal changes. The atmosphere of Mars is less dense than ours. Five pounds on the earth weigh only two on Mars. Water freezes at higher temperatures. The melting of the snow-caps in a planet where the mean temperature is only minus 36° Centigrade has suggested to some that these snow-caps consist of frozen carbonic acid, but the thinness of the atmosphere admits of rapid seasonal changes of temperature, and it is probable that a comfortable summer with rather cool nights prevails in the Martian tropics. Mars as seen from the earth varies from one to about seven diameters, therefore, from one to about 49 in area. It is clear then that the most successful observations must be made when the terrestrial aphelion coincides as to date with the Martian perihelion. The opposition of Feb. 9th, 1916, was not a favorable one, since the distance of Mars from the earth was over 62,000,000 miles. Throughout a long winter of many months, no sunlight falls on one pole, but on the opposite one a midnight sun prevails for a corresponding period. When the planet has reached the opposite segment of his orbit the relation of the poles to the sun has been reversed as is the case in our earth. Mars has received attention out of all proportion to any astronomical interest attached to the second smallest of the planets. His human interest accounts for this. Is he peopled? If so, do his inhabitants know anything about us? The earth is nearly four times as large, viewed from Mars, as Mars appears to us. But this is offset by the fact that when we are nearest to them, in order to look at the earth they have to look against the sunlight and see only the least crescent of the earth's surface, since its illuminated hemisphere is sunward and the Martians are on the shaded side of the earth , and cannot see it at all. They are in relation to us much as we are in relation to our sister planet, Venus. As to whether there are inhabitants in Mars, we know that though the mean annual temperature is very low, the sudden changes in temperature would be well understood and could be, predicted to an hour with approximate accuracy. The inhabitants could practise a systematic mobility. Migration with the seasons would be as common and as natural in Mars as to lay in coal is to us. If there are inhabitants, they probably adapt themselves by social organization, migration and irrigation to the suddenly changing temperature, water supply, and climate. It is always summer somewhere on Mars, and summer is probably a pleasant season with cool nights. The air is clear, the skies light-blue, the weather dry. The whole climate is airy and light. To those who desire a startling glimpse of the ingenuity of an alert mind in astronomical fields, and who are specially interested in the processes of such investigations, no more interesting works could be recommended than those of Prof. Lowell, of Flagstaff, Arizona. His books dealing with Mars are unique in that field. One would like to believe the theory of Prof. Lowell, and people this companion world, our nearest brother, no less than our nearest sister Venus, with happy souls who live and love, feel a subtle communion with us and are glad. The moons of Mars are of great interest. Two have been discovered, Deimos and Phobos. Deimos is probably about 25 or 30 miles in diameter and four Martian diameters from its primary. It revolves around Mars from west to east in 30 hours, but the revolution of the planet in the same direction in 25 hours gives Deimos the appearance of traveling slowly from east to west. Thus if Deimos were a new moon soon after sunset, the next evening at sunset he would still be about five hours up the western sky and would show a considerably developed crescent. He passes through all his phases at each appearance, remaining above the horizon about two days and a half, then disappears for a similar period. He is never seen more than 69° from the Martian equator because of his nearness to the planet. He is frequently eclipsed and often transits the sun. Phobos is probably only about five miles in diameter, and revolves at less than one Martian diameter from the surface of the planet. It completes one revolution in about seven hours, and meets Deimos in the sky (as seen from Mars) at each revolution. It rises two or three times during each night, and almost every night is eclipsed once or twice in Mars' shadow. He is not seen from Mars beyond 35° of latitude north or south. . He passes through all his phases each time he crosses the sky. Phobos frequently eclipses Deimos and both moons often transit or partially eclipse the sun. Deimos weald daren aboL one-centh of the sun's disk, Phobos only about one twenty-fifth. Mars must hold the record for eclipses. About 1,400 eclipses per annum are possible to the credit of Phobos and several hundred more to that of Deimos.

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