WHAT ARE METEORS?.

Taranaki Daily News, 19 November 1932, Page 1 (Supplement)

WHAT ARE METEORS?.

COMETARY WRECKAGE

(By

Rev. B. Dudley,

F.R.A.S.)

In view of the meteoric shower which, though expected, has not eventuated, it is not unnatural that inquiries should be made concerning the nature and behaviour of these bodies. As John Smith puts it, what are meteors, anyhow? They are generally small . dark masses or particles of matter, which circulate about the sun in swarms numbering many millions. We could never see them did they not happen sometimes to come near the earth and actually plunge into its atmosphere. This they do at such tremendous, velocity as renders them luminous, owing to the intense friction set up as they push the air in front' of them. Thus reduced to fine powder or vapbur, they settle upon the earth. On the average meteors are no large than pebbles, and weigh from an ounce upwards.

It has been computed that during a single night, taking the world round, there must be as many as 20,000,000 of them, though generally they are so feeble as to elude, ordinary notice. If those are counted which come within the reach of the telescope, this number would have to be raised to 400,000,000, to say nothing of those that are beyond the limits of instrumental power. It is known that meteors are not scattered together into separate swarms, and that • the - earth sometimes encounters these swarming myriads of stones. There is a close connection between meteor swarms . and comets; and the former, like the latter, are affected by planetary perturbation. They are pulled aside, that is to say, by the influence of nearby planets. That is why the meteor shower expected in 1899 did not eventuate; the .swarm was diverted from its normal course. There are good reasons for taking these swarms to be the debris of comets that are undergoing the process of breaking up. Hence, like comets, they journey round the sun in a givfen orbit, which is always' elliptical. It is when the earth and a swarm happen to meet and cross their paths that we get a meteor shower. ' The connection between comets and meteors is well established. The comet itself is a great ag’gregation- of meteoric particles and gases held together by gravitation. These, by friction or electrical repulsion, become luminous, presenting the appearance we. are familiar with. The .particles in gen-, eral, being widely separated, are at length,. under the. stress. and strain of opposing ■ forces, . dismembered and spread out in streams or swarms, individual particles / becoming meteors or “shooting r stars” as soon as they plunge into the earth’s atmosphere, as has been explained. . It will be seen, therefore, how’comets and meteor swarms-are associated. • .Halley’s comet, for example, has a meteor shower connected with it, which can be seen during' the-month .of May.every year. hr 1910 a few' meteors fell to the earth and were believed to be part of the debris of that comet. If this is so, writes Dr. Crbmmelin, “we can actually handle fragments of Halley’s comet.” In .the year just named, this comet passed over the disc of the sun.- But though a careful watch was kept in case the solid masses forming its head might appear as a kind of cloud,, nothing was observed. Had 1 any of - them -b een five miles or more in. diameter they "would have been visible. ..It was therefore concluded that they -were smaller- than -this,-/-arid could not- haVe. been closely cqffipacted; ■ . ; -Thb' speed of meteors before their motion finally is arrested by the atmosphere is roughly 1000 times that of a rifle-bullet. It is fortunate for us that their velocity is great enough to convert thfese stones into harmless dust- or vapour, thus preventing them. : descending , upon the Earth in a. rain of-solid pellets with results that can.-well, be .imagined.. Sometimes, however, meteors . are so large that they survive the •. atmospheric resistance, the greater 1 portion of their bulk reaching the earth in a solid state.' They are then known as “meteorites. Observed in the - act of falling,- these objects have sometimes afterwards been found buried a .foot or two in the ground, often too hot to be touched with the hand. ' Such, a body does not arrive at' the earth’s surface with the same planetary velocity it had originally, but with a greatly reduced speed in consequence of atmospheric resistance. Its final descent is little, if any, more than that of a terrestrial body falling from' a great height. This .is. so far true that the direction, of a spent m eteo . r when actually reaching the;/ ground is almost or quite perpendicular,, while the motion is- reduced to 400 ft, or- 500 ft. per second. A chemical examination of meteorites shows that, although in composition they differ from other natural products, their elements are all familiar to US, and they are all built up of the same, materials, while in each variety some particular element may predominate. :

Some interesting information concerning the great meteoric shower of 1833 is given by Dr. F. R. Moulton in his Astronomy, just published. One observer, he says, counted 650 of them in a small part of the sky in 15 minutes, while other coihpetent witnesses estimated that they. appeared at the rate of 10,000 an hour. Some, however, were so faint as to appear as but thin streaks such as one may see n any clear moonless night. Others were as bright as Jupiter or Venus. He quotes a report to the effect that one meteor was to all appearances nearly as large as the moon. The flashes at times were so vivid as to arouse people from slumber, and left .a luminous train that persisted for several minutes. Alexander von Humboldt’s record of the great shower in 1799 (November 11-12) is to the effect that thousands of meteors were observed all moving south, and that there was no part of the sky twice as large’ as the moon which was not crossed’ each. - instant by a meteor or fire-ball. /We now know the reason why the meteors Humboldt observed all “shot” in a southerly direction. Their radiant point was in Leo, which at that time was in such a position in the heavens as would require this motion viewed from Cumana in South America, where he was exploring at that time. In all these showers the meteors appear to radiate from the same noint on the celestial sphere. In other words, if their trails are prolonged ’backward they all pass through a point called the “radiant point.” This remarkable property is a consequence of the fact that all of them are moving in parallel lines through the earth’s atmosphere. If a’ diyer were to make a sudden plunge through a shoal of fishes, as he shot headlong forward the fish would appear, even supposing none of them to actually move, to radiate in all directions from a point immediately before him. In like, manner the earth plunges through a meteoric swarm with the visual.result. under consideration.