FASCINATING COMET.

Taranaki Daily News, 28 December 1929, Page 17 (Supplement)

FASCINATING COMET.

RELATIONSHIP TO METEOR.

(By

Rev. B. Dudley,

F.R.A.S.)

My last contribution on the subject of comets dealt with these wanderers as being in the main members of the solar system rather than comers from other spheres infinitely distant from the sun. It was shown that their orbits are frequently shortened owing to their being captured by. the larger planets; and something was stated-.concerning their, great speed and size/ The present article deals, with further matters of interest relating to these strange apparitions. If the celestial venturers under consideration are enormous in bulk, they are nevertheless of but little mass. “Mass,” indeed, seems scarcely the word to use in describing them. It has been estimated that if all the comets seen in the history of mankind could be solidified and combined in one, the whole would make up a body much less in size than the moon, such is the tenuity of their structure. The nucleus is, in fact, nothing but a swarm of meteoric particles, although it is difficult for us to form an idea of the actual size of the particles. These cohere, of course, by ..gravitation.. One of the reasons. for thinking that the head of a comet is, in part at least, composed of solid particles- lies in the fact that it acts as though influenced by gravity alone. Another is that an intimate connection is known to exist between comets and meteors. These latter are, as one specialist says, “lumps of iron or stone, which are travelling round the sun on paths that have been found in several cases to coincide with cometary paths, whence it is concluded that they are cometary debris.” Their total weight, he further states, is too small to keep them together by their mutual attraction, so “each separate lump is really revolving in its own orbit about the sun, but the orbits of all are very nearly the.same, and the comet may hold together for long periods.” Halley’s, for instance, has continued for more than two thousand years, and shows signs of lasting for an enormous time yet. It must eventually, however (according to theory), owing to the differences of the attraction of the sun

and planets on different portions of the swarm of particles of which it consists, disintegrate and become widely dispersed until it is beyond recognition. The disturbances which make for dissolution operate chiefly when the strange guest is in the neighbourhood of the sun. When here gravity, electrical repulsion, and possibly -light-pressure, combine to treat .the visitor with indignity and tear it to pieces, each force operating differently and on different particles. A comet’s tail is made up of material particles and of gas, both in a finely divided state, the gas being driven out from the head by repulsive forces in the sun which operate more strongly than gravity. This predominance of repulsion over gravity could only occur in connection with particles that are exceedingly small, approximating to 1/50,000th of an inch in diameter, in other words, comparable with a wave-length of light. The matter forming the head consists of much larger particles, and would be unaf- . fected by such non-gravitational forces. Put summarily, the case is as follows: The connection between comets and meteors is well established. The comet itself is a great aggregation of meteoric particles, held together by gravitation. These, by friction or electrical action, become luminous, presenting the appearance we are familiar with. The particles in general being widely separated are at length, under ' the stress and-strain, of opposing forces (named above) dismembered and spread out in streams or swarms, individual particles becoming meteors or “shooting stars,” when they plunge into the earth’s atmosphere with tremendous force and are reduced to vapour. When, however, they actually reach the earth's surface as solid masses, eseaping vapourisation, they are known as meteorites. In 1920 a few meteors fell to the earth and were believed to be jtart of the debris of Halley’s comet of that year. If this is so, writes Dr. Crominilin, we can actually handle fragments of Halley’s comet. During the year just mentioned this cornet passed over the disc of the sun. But though a careful vigilance wits kept in case the solid masses forming its head might appear as, a kind of cloud, nothing was observed. Had any of them been five miles or more in diametei they would have been seen. It was therefore concluded that they • were smaller than this, and could not have been closely compacted. Halley’s comet has a meteor shower associated with it which can be seen during the month of May, in early morning hours. It is estimated that millions of so-called shooting stars enter the upper air every day, though the naked eye sees only the more conspicuous of these meteors. Professor Newcomb computed that a million tons of these particles are swept up by the earth every 24 hours, so thickly is space strewn with them. It has been suggested that the Zodiacal Light, too, consists of meteoric and cometary debris. This being so, particles that form the Light do not revolve round the sun in circles, but long ellipses, the actual particles composing it continually changing, thus accounting for the capricious changes in brightness of tho Zodiacal Light. If Messrs Chamberlin and Moulton are right in their conjecture that the near approach of another sun to ours mil' lions of years ago caused the distri bution of matter in our system into a spiral, then comets, meteors and the Zodiacal Light are the fragments of the spiral which had remained unattached to any planet. Comets have told us much about the . cosmic order —that part of it, at least, to which we belong —and may yet bring us further valuable and interesting information. Every new comet is studied with the minutest care in the hope of ] this. It is long since Aristotle said, “Man only realises himself when ho knows that he forms part of something incalculably vaster than himself.” These wanderers tell iis of the vast- • ness of the scheme of Mature.’