ASTRONOMICAL NOTES FOR FEBRUARY.

Press, Volume LXVI, Issue 13645, 31 January 1910, Page 6

ASTRONOMICAL NOTES FOR FEBRUARY.

(By the Rev. P. W. T'ktrclovgvi, F.R.A.S.) ■

February is the hottest month of the yer-r in the Southern Hemisphere. The cause of this is that as long as the earth receives more heat from the sun during the day than is loet at night, the heat accumulates, though the daymay bo getting shorter and the sun's rays more oblique. In March the balanou passes to the other side, and the temperature" rapidly falls. The cold than increases until long after the slicrtest day, in, fact until the receipts aro again more than the expenditure.

The beautiful Venus is now. lost in the sun's rays. Mars is still with us, but greatly waeted in splendour. Jupiter, however, is now rising about ten o'clock, and will soon be the pride of tho evening, as he rises a few minutes earlier every night.

Mars has been the subject of some discussion during the past month. One cable informed us that Mr Alexander, of Greenwich Observatory, stated in an address before the Astronomical Society that Professor Hale's 60 inch telescope had proved that the "canals" are an optical illusion. That statement may be token with a grain of salt. Hale'e telescope at Mount Wilson ie a reflector That kind of instrument does good •work in the observing of stare, which are mere points of light, but it has its reputation yet to make in studying ine details of the surface of planets. ISo many good observers in different parts of tbe world have seen the canals, and their maps and drawings accord so well with one another, that the optical illusion theory is extremely difficult to receive. Some of the more conspicuous lines have actually been photographed, and they 6ay that the camera cannot Us. ' .

Professor Lowell, the author of the popular book entitled 'vMars," and the leading advocate of the irrigation theory, goes to the opposite extreme. Hβ claims to have seen a new canal; not merely one that had hitherto escaped observation, but one that was not there before, a newly-fini&hed one! A few days later we were informed that Lowell "cays that the- new Martian canals are strikingly evident, and denote the presence of an animate will." By the former part of the sentence he means that the new features axe so. conspicuous that they could not have escaped observation had tbty boon th«ro all the while. It will he very difficult, however, to satisfy astronomers on .that point. Several claims have been made to having discovered tiny new craters on the mpon. But, though the objects may not have been marked down on any of the num-

erous lunar maps, astronomers axe by no means certain that the craters were new. They may simply be "uncharted rooks. ,. Professor Lowell, however, claims that his new canals are not minute strealcs that might easily have been overlooked, but that they axo "strikingly evident." Mr Alexander will probably say, "The more striking the new canals are, the more are they likely to be illusions." Other critics may remark that it takes a long time to construct a canal hundreds of miles long, and that it is imposeible to be-! lieve that the Jlartians have constructed tbceo new objects in the two years that have elapsed since -the last opposition of Mars. Professor Lowell would) reply that the construction may have been in hand for any length of time. What is seen is not the ditch, but tho wide belts of vegetation along its sides. These, lie would claim, now appear all at once when the canal is finished and the water turned on. Tho objector would possibiy reply that intelligent beings would -want to use the nni&hed part of such a great work long before toe whole scheme -was completed. A transcontinental railway is not opened all at once from end to end, hut stage by stage. Still more sensational have been the

suggestions from Mr Cromelin., of Greenwich, that tho earth might possibly pass through the tail of Halley'e comet. Hβ added that the passage would be harmless. This is the kind of thing that scareT-writOTs lore to get hold of. Happily, the days of comet scares are over. Time was when European goTenuneuts hod to ask their astronomers to publish something to allay the popular terror. Everything mysterious is terrible, as Culgascus remarked. Knowledge, however, has shorn the comet of its terrors, and reduced it to perfect harmlessness. It is to be hoped that we will pass through the tail, for it will be an event scientifically interesting. We will, however, not know anything about it until the astronomers tell us. Grout efforts have been made to fix the date of the perihelion paesago of the comet, but no one knows to a day or two. Mr Cromelin has himself been very industrious in the matter, and if his date ehould prove to be correct the suggested passage may come off. TLo orbit of the comet does not lie in the same plane as that of the earth. They cicss one another at a considerable angle. If the earth and the comet should both reach the crossing point at the same. time, then the visitor wojild be directly between us and the sun. The comet", in fact, wonld tiansit the sun. It is very doubtful, however, whether so tenuous an object could be seen against the sun's face But supposing the transit to take place, the tail, which always points directly away from the sun, would, if long enongji, reach the earth We should say that the chances are enormously against the accurate timing required to bring about the passage through the tail. The next question is, what is the tail of a comet? The prevailing belief now is that it consists of a cloud of extremely fine particles of matter that aie repelled or blown away hy the rays of light from the sun. These particles are about equal in size to the minutest object discernible in the most powerful microscope. These particles flitter in the sunlight and make the luminous tail. Everyone knows bow small particle 3of dust gutter in the sunbeam that penetratej mto a dark room. The tail matter is finer than the dust of the room, and the particles are not nearly so close together. Tiny stars that the faintest vapour would hide can be seen through 1,100,000 miles of tail. It is probable that the matter in a cubic mile of tail could not be weighed in the most delicate scales known to man. No means of weighing a comet are known. It is, however, certain that the largest of them are of altogether insignificant weight or mass, among astronomical bodies. Probably if Comet could be condensed into solid blocks, one of our ocean steamers could take it for ballast. If the whole comet plunged into the earth, there would probably be a glow in the sky, perhaps a shower of shooting stars, and vl\ would bo over.

Now bodies of small masa cannot retain gases, especially hydrogen, in a free state. It is doubtful whether even th. attraction of the earth is sufficient to keep free hydrogen from flying ott' into space. Asteroids have no atmosphere, the moon has none. It is thought that no satellite.has any. Mercury possibly has none, and Mars seems to have very little. All this, means that small and light bodies cannot retain an envelope of gas. It is therefore ridiculous to talk of the comet pouring out

a deluge of hydrogen, or of any other .gas It has no gas to pour out. But if it had, if the tail were all hydrogen,", or all carbonio acid gas, and if the whole of the tail were poured on the earth, how much oxygen would it neutralise? Not one billionth part of the encrmous ocean of it that is in the atmosphere of the earth.

We have not yet heard of the "Transvaal Comet" being seen in New Zealand, but we know of no reason ■why it should not be seen, except tha<« the mornings have been cloudy, that there is a bright moon, and that the comet itself is fading rapidly. The photographs of Eros, the asteroid that comes nearer to us than Mars, have been carefully analysed with a view of ascertaining their evidence as

to the distance of the sun. The result

is to increase the accepted solar parallax from 8.80 to 8.806. This reduces i&e distance by about 6000 miles.