IN STARRY SKIES

Evening Post, Volume CXI, Issue 107, 6 May 1926, Page 17

IN STARRY SKIES

LOST COMETS

INFORMATIVEIEVENTS

(By "Omega Centauri.")

Several comets have broken into fragments and subsequently disappeared. These have thrown a flood of light on the constitution and life history of this mysterious class of bodies. Although the 'complete disintegration of a comet and its consequent loss of identity was not proved until last century, earlier observations of this tendency are recorded, v In\"The Story of-the Comets," Chambers mentions •' that Seneca, on the authority of Ephcrus, states that the comet of 371 B.C. separated into two portions which followed different paths. He also records that /status noticed in the comet of 11618 an evident tendency to break up. When it first appeared it was a single nebulous object, but 'some weeks later it consisted of several small nebulosities. 'In 1770 Lexell's comet came within ■ c and a half million miles of. the Earth without having any perceptible effect on its motion. It, however, did not escape so easily. It was considerably delayed by the Earth's attraction. nd its orbit distinctly changed. When found it appeared to be moving, in an elliptical orbit with a period of five and a-lialf years. On its next return it was: probably on tho opposite side. c:° the'sun> and quite naturally it was not seen. But if it had not suffered any further serious perturbations it should haye beeii; observed many times since then.' Calculation, however, shows that on its outward journey from the Sun inM779 ,it invaded the system,; of Jupiter. It passed amongst the satellites without producing on them any effect which could be detected. Its own orbit, however, was so radically changed that it has :never since been seen,; or if it 'has been seen it has not been identified, ...'■/.• „ Liaio, a French observer in Brazil, ml February,.iß6o, discovered a comet which w^s.; aeftoinpaniodeby a fainter nebulous mass. '! Nothing further has been seen of it. < • ■'■.•.''-■ ' The second comet of 1881 threw1 off a fragment,'which became for a short, time an independent comet. .After a few days it was lost sight, of completely. •''..'■■'- "■':---. Swift's comet of 1899 was observed at Lick to become double, and in the course of a fortnight the two portions saparated gradually until they were 29 ' minute's of arc apart. Bredichin calculated that both nuclei were pursuing ! -perbolic paths* that of /the smaller having tho greater eccentricity. '■■■ But by far the. best known, iiutance ',of ,e6metary disintegration .is, that of Jiela's comet, which was discovered by Biela on 27th February, 1826. It was then' very faint..; ;Tcn days later it was seen by Ganibart.' Altogether it was kept under observation for eight weeks. The -• elements ; of its orbit were -calculated '••both by Pielaand Gambart,'who found a period for it between six and a halt and six and two-third years.. They noticed fV similarity, between the elements they found and those of'two earlier comets. The first o£ these was the cornet dis r covered by Moiitaigne on Bth..March; .1772, amd afterwardsobserved by Messier. Tho other. w£s the comet discovered by ,Pons on lOth: November, 18.05^ The latter' increased in;.brightness until it was nearest to the earth on Bth DecenibeT, when it could be seenCwith^ out a telescope. Besscl and others calculated its orbit and pronounced it elliptical.; Its identity with Montaigne's comet was suspected. Biela'proved the identity of his comet with each of these; Sant'ini and Dainoiseau announced that it would return on 27th November^ J832, which it did punctually ,to the-'v-jery day. This was the second instaneq. of a comet returning at the predicted jtime. : A panic' was .caused by the announcement that the comet would cross ; ;y'the earth's orbit, although ' astr.tmo'mers ■knew that the earth would: be a full • monthi'3 journey away from, that spot at : the time.' lOlbcrs had pointed that out .in. 1828.: .-. .•-;.-;- Sir J. Herschel Watched this comet pass in front of; a star cluster, and did not notice that it had any obliterating effect. ' Every twinkling point could be seen through the comet. Sir W. Herschel in 1807 had noticed that- stars seen through a comet's tail lost some of their ' lustre. Biela's comet was liot seen iv 1839, being unfavourably placed for observation, but its next return forms a landmark in cometary history: Towards the end of 1845 it appeared. On 28th Novomber, it showed only as a-faint nebulosity. On 19th December, Hind noticed that it had become, elongated and appeared pear-shaped. Ten days later it had definitely divided into two. A sketch made by 0. Struve on 19th February, 1846, suggests dignity arid impudence. The two comets are parallel side by side. The main one has an immense head and a comparatively narrow straight tail. The other is a diminutive copy of it;; By 3rd March, 1846, the two nuclei were 160,000 miles apart. The two comets returned in 1852, but their distance apart had increased to 1,272,000 milds. The comet was due to return in May, 1859... Separate orbits were calculated for the fragments and.a close watch was kept. The comet failed to appear. The same occurred in January, 1866, although it should then have been very ;f avourably placed in the heavens. In. 1872 apprehension was again caused, by the expectation that'the comet if it.still-existed would come very close, io.the earth. 'Most astronomers, had already given it up as lost. But Klirikerfuos, of ■ Gbttingen, kept. iiia, attention fixed oh the subject and was rewarded; Though the comet again failed to appear -.there" was a fine meteoric display ..on 27th November, 1872. -The-meteors came from a -radiant:, which corresponded with;, the ; position ■ the comet should have occupied twelve weeks bofore. Then Klinkerfucs sent a remarkable telegram to Pogson at-Mad-ras. It was worded :as follows:— "Biela touched earth .on the 27th. Search near Theta Centauri." Pogson did search, and the : result was most extraordinary. He actually discovered a comet there. Unfortunately bad weather prevented its orbit being calculated. Subsequent study, however, tended to' show that it could hardly have bcon either of the known fragments of Biela's comet, but that it may havo been another, comet moving on the same track. This is an example of what are known as comet groups. They seem to deserve the nam. ..family more than those to which it is applied. These comet, groups are supposed to have been formed each from a single g'gantie comet. -The families associated with the planets oil tho other hand have been captured and collected by the planets and may have had widely different origins. If, however, we adopt the'theory advocated by Prbetor and by Grommelin that they have been ejected by the p'.nnets they are fully entitled to the name family. But to return to Biela's con:-t. Again in IS.'-O and in 1885 it ivas conspicuous by its absence. But in 18S5 there was another magnificent of meteors on 27th_Noyember. *It was

calculated that 75,000 meteors per hour could be seen. During the height of the display a piece of meteoric iron fell at Mazapil in Mexico. Tnfortunately its owner, to whom we are indebted for its description, did not actually see it fall. But he did see it whilst it was still llojt~..enouglj.;.,to glow. It weighed 3864 'gfanis-'jiha made a hole 30 centimetres deep. Lowell speaks of it as eight pounds worth of nickel-iron, and says hat it contained graphite enough to write its own history, only, unfortunately, it could not write. Had it done so we should now know more of Biela's comet then we do. In 1885 Biela struck earth even more literally than, it did. in 1872. In 1892 the meteors cajrie again, but six flays earlier. The changed of date from the 27th to the ;23rd was found by Bredichin to be due to ■■ the action of Jupiter on the swarm, t. •. These November meteors are called Andromids from the position of their radiant, or Bielids from their origin. Looking back it is found that observation's,", of the Andromids have been made ever since the eighteenth century. The date' has changed from 7th December to the end of November in perfect; accordance with the retrograde motion of the crossing point of the earth's orbit and that of Biela's comet. In 1798,. 1830, and 1838 the showers preceded thd comet along.its track; in 1872-we have seen they were far behind it. It .appears that meteoric particles must 4be thickly distributed in vast numbers, along the comet's orbit over.a length of at least.soo million miles. Meteorites are said: to have fallen ■ on' several other occasions about the vend of .-.November. As long ago as 1861 Kirkwood wrote: "May not our periodic imeteors be the debris of ancient bttt npw disintegrated comets, whose'material has become'distributed around, their orbits." He. made a list: of eight cornets, which: were then known to h'avo divided iii a manner similar to that shown by ißiela's, and then to have disappeared. '