ASTRONOMICAL NOTES FOR FEBRUARY.

Press, Volume L, Issue 14889, 31 January 1914, Page 10

ASTRONOMICAL NOTES FOR FEBRUARY.

(Bt the Rev. P. W. Faibclough, F.R.A.S.) Mars is now probably the brightest star in tho sky, for he i 6 near opposition, and at his least distance in the present apparition. He is easily distinguished by his superior light and his red colour. Saturn norths more than an hour before Mars, and will still bo found under the Hyades. He is a bright star of a pale white colour. Jupiter has now sunk near the sun. For the constellations, readers are referred to our maps, which appear from time to time in the "Weekly Press." Last month, by the way, a slip of the pen made us say that tho top of the map represented the zenith. That was an error. The rectangular maps are always to be turned upsidedown, so that the top represents the northern horizon. The "Illustrated London News" has been giving some very effective drawings of the planets on a large scale. In a recent number the south pole of Mars is set beside the earth's south pole, in such a way as to suggest great

similarity. In a superficial way this is correct, but th© planets are made to appear too nearly of a size. Mars has only half the diameter of the earth. I But the great nnlikeness lies in the fact that the Antarctic ice and snow are perennial, while the "'snow" of Mars may entirely disappear during his summer, though the sun's power is not half as great with him as with us. This proves that the Martian "snow" is little better than a heavy trost. Professor J. W. Gregory has been discussing before the Geographical Society the question whether the earth is ' drying up or not. He considered the evidence derived from plants, from the traces of floods, and from the ancient habitations of man. It is clear that some regions aro drier than they were at an earlier stage of the human period. On tho other hand, some other regions are evidently wetter than they once were. There is therefore no evidence that there has been general declino in the rainfall since man has been on tho earth. Thero cannot bo any failure until there is a failure of the solar radiation or a vast extension of land surface at tho expense of the ocean. It was recently cabled that Professor Doolittlo had calculated that the sun would fail in about five million years. That topic is therefore not urgent, so wo will hold it over till somo other matters havo been considered. A. G., Hawke's Bay, writes:—"l would be much obliged if you would kindly explain more at large your statements about the Leonids and tbe rings of Saturn. Of course, I accept them as correct, but I would like, if possible, to know the reasons at the back of them." The famous November meteors that gave tremendous showers of shooting stars in 1833 and in 1866, but failed in 1899.. are called Leonids, because they radi-ite from tho constellation of Leo. Leo is called the "Sickle" by the English; it may be seen in the north-east about 10 o'clock. The meteors radiate from the space round which the blade curves. The great displays of history proved that they had a period of 33 years. A few meteors from the same region were seen in preceding and following years, and it was inferred that tho swarm of littlo bodies wore dispersed along an enormous length of their orbit, but were condensed in that portion of the flight that happened to cross the' earth's orbit in November every 33 years. The vanguard were seen in the preceding, and tho rearguard in the succeeding years. This cluster was called "the gem of the ring," and the action of planets in expediting the neaTer end of this long "gem" tended steadily to. attenuate it. In 1599 the display was quite ordinary, much to the disappointment, of millions of spectators; for the event had been predicted, as it had been in 1866 when it was so splendid as to. be terrifying. Whether the "gem" had not quite arrived, or had just passed, when the earth reached the cross roads, or whether some disaster had overtaken it. is not certainly known. But if it can be proved that the "gem" passed near to Saturn, the mystery would be explained. The meteors are no doubt the wreck of a comet, and like comets of the ''family" of Uranus had a period of 33 years, more or less. Each, of the great outer planets has a family of "captures." A comet or a meteor approaching the sun from outer ■ space has acquired a considerable velocity by the timo it reaches' tho planetary orbits. Coming from infinity, it would move 4.7 miles per second at Neptune's distance, 5.9 at that of Uranus, 8.3 at Saturn's, and 11.3 at Jupiter's. We suppose that the body comes from infinity for the sake of the argument; ,if it came from a lesser distance the motion acquired under the sun's pull wpuld bo less. Suppose now that a comet with a velocity of 5.9 miles per second arrives at the orbit of Uranus while the planet is in that neighbourhood. In some cases he would expedite it, but in others ho would retard it. Halley's comet has been detained for -nearly two years by Jupiter. Suppose Uranus to hold the comet up so as to deprive it of nearly all tho motion it had acquired. It would in that case practically have to start again. A stone falling from a cliff, if it lodge on a projection for a moment, has to start afresh, and does not Teach tho bottom with the momentum it would have had if it had not been stopped. A comet or other body moving to- [ wards tho sun is liko a switchback railway. If there were no friction tho car would gather sufficient momentum i on the down slope to carry it up to an equal height on tho next.rise. Thero is friction, however, and the car mounts only to a lessor height than that from l which it started. In tho case of the comet there is no friction—unless a planet interferes. The comet acquires sufficient momentum in its fall to perihelion to carry it back to the distance from which it started. If, therefore, it had to start afresh from the vicinity of Uranus, it can only acquire sufficient velocity to carry it back to the region whero it was interfered with. Now tho meteors begin their fall back to the sun from about tho distance of Uranus. From tho moment they reach the extremity of their orbifc they begin to return, but the pace is extremely slow. They acquire only the microscopic fraction of an inch of velocity in tho - first second, but they go on adding an increasing amount to their speed every succeeding second for the next 16. years, till they reach perihelion. If they fell from exactly the distance of Uranus straight into the sun they would reach him in 14 years and 8 months, but they go somewhat beyond the planet at one end, and at tho other sweep past the sun and reach their nearest point on tho further side of him. Hence they tako longer than the direct fall would. Now our meteors in falling back from Uranus have acquired a velocity of about 2_ miles per second by the time they reach the orbit of Saturn. If the planet is there to meet them, woe betide them. He is a powerful body, 95 times as massive as the earth. For millions of miles around he ,is more powerful than the sun, just as tho earth is for nearly one millionSaturn swings a moon 8 millions of miles away. His nearest moon is 117,000 miles from the centre of planet, but has to move 9 miles per second, moro than 14 times as fast as our moon. The rings are clouds of tiny moons, or meteors. They are so close together that they look solid and aro as bright as the body of the planet. Still, the 6un shines faintly through them, for the rings are only about fifty miles thick, thouch they are 173.000

miles vacross. Thero is a '«*-_> between tho great planet and the _rs_ bright ring of 18,000 milos, then comes •■'* a flat ring 17,000 miles wide and 50- " thick, then a gap of 1800 miles wi_„ "'■ and then another ring 12,000 milS { wide and 50 thick. The p__net-is ' 75,000 miles in diameter, or so to- •' j speak, 1500 times as thick as the *' ring.. If an orange be taken for tha planet, then thin paper will do for the "'' rings. Between the planet and tha fir_ bright ring there is a wide but dim ring called tho "crape" ring. H cannot bo seen with small telescope, for it is composed of moonlcts, or meteors, thinly spread. Perhaps some - of the main army in the bright rings have beon crippled by friction or «C sion, losing part of their velocity and have fallen inward. It was long knom. from pure reasoning that the ring* could not be solid, for if they wer* Use part nearer the planet would mo _ much slower than the part more* _. mote, which would be contrary to tha law of gravitation. A few years ago - the spectroscope showed that the outside moved 10 miles per second, and tho inside 12 miles, which is what the • law requires. We have therefore in : Saturn's system a tremendous «_.- gino of incalculable power, with its - sky-spanning fly wheels whirling at an unimaginable speed, and its ten moons flying in endless circles. Into this awful vortex come our poor little gnats of Leonids at a snail's pace of 2. miles per second! What is going to happen to them? Their chance is infinitely less than than of Stephenson's "coo." .*-■ Saturn could not capture them with- ' out the intervention of a third body, " ' but if some of his moons lent a ha_d| of if the wanderers touched tbe rings', they, or a large section of thorn, wouW ,' never revisit our November skies. Hs would bind them in somo kind orbit, or draw them down on himself. If' however, neither moon nor ring co- • operated, he would simply fling them into some entirely strange path around the sun, possibly depriving - thorn of the old velocity necessary to ' take them back to Uranus and com- '-'- pelling them to return every 12 or 13 pr years to the place where ho caught -'' them. . -"

Of course, as the meteors are spread along hundreds of millions of milea <_ ~' the old orbit, what has here been said ' will apply only to that portion of the_'__ that might trespass upon Saturn's do* V main while he and his retinue marched by at his measured pace of 5.9 miles per second. If such an encounter has taken place between Saturn and the"' '" "gem" of the ring of Leonids, thin farewell to the great November displays of celestial fireworks. Saturn l may have destroyed them, hut that * they should be able to cast any portion - of him, or his, into the sun is cally impossible. Particles of tho rings " could .escape from Saturn only by being expedited, and bodies moving at S\ . miles per second cannot expedite'bodies . moving at 10 or 12 miles per B_eon., '' r any more than a bullock-dray can expedite a railway train. Tho slow body . can only retard the swift one, and to >' ' retard particles of the rings is to cause -' them to fall towards Saturn. . T_e '' critioal velocity, or the velocity of «s- • J cape, is found by multiplying.the or-. " bital velocity by 1.414. That is, tbft; outer edge of tho rings would, hats io .. be struck so as to increase '.its velopity "- from 10 to 14,14 miles per second. That - velocity would carry a fragment-f_qm »:"; the outer edge of the rings beyond tho planet's control. It would-then per-.-J sue an orbit round tho sun, and would . not fall into him. - ■>'.■; An interesting letter in "Tho Press"*"' -\ few woeks ago, Mr J. C. Andersen said '"' i that it was claimed on behalf of the , * ! ancient Maori that he could, see at* ..... least two of the moons of Jupiter, knew that Saturn wore a circlet. Ide ''• not question that the claim has" been *-.. made. But when was it first madtP__"=*. As sailors were the first whito men \6 '"_ mix with the' Maoris there.' is' littl*_-,. doubt that tho Maoris would hcar''pJ/the discoveries of the white man t before any collector or observer «et;\_ down the uncorrupted lore. The Maori. would not let the pakeha hare alt ths- \ boasting, and that is,how I would• ox* plain, tho two claims in question. It*.•-';■! is conceivable that someone who kne 1 . >g that there were moons to look for may have actually seen somo of them' wit. '*'-.'; the naked eye. But' it could only be W~f% some process of hiding tho glare of.l the planet from the eye. Many have : *-J claimed to see the moons, but no one' ~-- has yet stood tho test of an cxamin.-/:1 tion. Bat while it might bo possible.' P to see ihi& moons it may safely be de-.- * nied that it is possible for any _____-»', eye to see Saturn's rings unassisted* y'? Tho radius of tho space within the ',; luminous ring of Saturn, is only about . _ 53,000 miles, and 35,000 of that is oe- ■-* cupied by the radius of tho planet. It ■-'_ required, therefore, to see a space of * t 18,000. But the whole diameter of tho . y rings is 173,000 miles. Yet a gcbd :." eye, multiplied several times hy optical ; aid, cannot distinguish this enormous. ; surface from a star! How, then, is any -. eye going to 6ce two little holes in .- the surface? The distance of the outer '- of th© "old moons" of Jupiter from J the surface of tho planet is 543,000' miles. The distance o£ the next moon, ." tho largest one, is still 288,000 miles* Both these moons are within the ■•' limits of good vision, but are lost in the blaze of tho planet. If, then, men cannot see spaces of 5-13,000 and 288.C00 miles, how is the Maori to see - spaces of 18,000 miles which are twice . as far away as Jupiter? The rotatioe period of Mars, referred to in tbe cable, will be considered next month.