HALLEY'S COMET.

Bush Advocate, Volume XXI, Issue 286, 7 June 1909, Page 7

HALLEY'S COMET.

KXl'TCCnj:i> IN JAMWKY NKXT. In Science Progress for Ajivil, slr Andrew C. !). Crominelin, 15. A., F.U.A.S., narrates the hi.sterv o'i i! alley's comet, which is expi-vf'-d to n>ake ajv appearance in <>ur v kios early next y(>ais This reiusr K.-iMe member of tin- sun's family c<..hi)lclPsits revolution in about tin eequrrters of a century. Its last appearance was in 1535, ancL is thus- described: "The comet was first seen by M. Diimouchel, Director of the Observatory of tbe Roman College, on August o, 1885. It passed its perihelion on November 16, and remained in sight till the following May, its changes of appearance being carefully followed by astronomers all over the world. Though not equal in splendor to tlie greatest comets of the nineteenth century, such as Donati's in 1858, or those of 1811, 1843, 1882, it was, nevertheless, an v extremely interest j^g object, from the rapid changes which it underwent from night to night. In this respect it seems to have closely resembled comet Morehouse, which lias just passed out of reach of Northern', observers, but is still Under observation in the Southern Hemisphere. The nucleus in. each case appeared to be in a state of great activity, and ejected streams of matter in various directions with a. violence that Has been eomjiartxl to a volcanic outburst. These streams are at once repelled by tlie sun, the repulsive force being simply the action of light oir very finely divided matter. The. main tail is directed almost exactly away from the sun, but there are a number of lateral tails or brushes, making various angles with this. It was shown by Bessel tliat some of the changes, could- be explained by supposing that the comet was rotating in about five days, and a similar suggestion was made for comet Morehouse. A difficulty arises in supposing a body to rotate that, is neither a rigid body nor held 1 together by a strong' central force. However, it seems that a rotating head would . produce a semblance of rotation in the tail streaming from it, although the separate particles of the tail are not rotating, but simply driven outwards. "Dr Smart has prepared an ephemeris for its motion in 1910. It >s based on the supposition that tlie perihelion passage will be on April *16, 1910, a- date which I consider the most probable, though it is right to add that some authorities give dates as much as two months later. It will be nearly stationary in Pisces in January and February, and probably visible with -small telescopes, possibly even with tbe naked eye. It 'will then? pass behind the sun, being a •fairly bright morning-star r in: April tiucl tlie beginning of ' May.. It ay ill again pass the sun on 'May 17, 'rind for a few days after this may-be'ex-pected to be at its greatest splendor, being 12,000,000 miles from the earth. In consequence of this ii,ear approach, its motion will bo very rapid, and it will pass in a few days from Taurus to Hydra, and Sextans. It will, unfortunately, be south' of the sun, which will grea.tly impair its splendor as seen from England, though in tbe Southern Hemisphere it is likely to make a good display. The. circumstances as regards its position in the sky are very. like those in 1866, when it made such a sensation ; but in all probability the comet has lost much of its glory in tbe interval, so that not too much should bo expected next year, though we are quite justified in hoping for a. fairly conspicuous object, with a tail several degrees in length, probably in. a state of- rapid change, as in 1835; and with the aid of the. spectroscope and the camera we may hope to interpret these changes much more fully than was possible then. But, apart from its intrinsic splendor, the comet has such an interesting history, and links the centuries together so wonderfully, that no one gifted with the smallest degree of imagination can fail to follow its course with the deepest interest, and renewed admiration for the great English astronomer whose name it bears, and who discovered !ts periodicity in such a brilliant manner."