SCIENCE UP TO DATE.

Lyttelton Times, Volume CXVII, Issue 17251, 19 August 1916, Page 13

SCIENCE UP TO DATE.

‘DOUBLE STARS ONCE MORE.

(By JAMES COLLIER.)

Wo hare already told the story of the double stars, so far at least as concerns its beginnings in the hypo thesis or the oirrhteon-vear-old Gnericko explaining the phases of Algol, the more ■thoroughgoing work of Sir W. Her--,clv?l a,nd' the comparatively recent application to it of the results of spectrum analysis. Rut very much has been accomplished' in this most rascinating hold, and some striking developments are ‘fraught with such deep significance as to invito exposition. THEIR ORBITS. Let us go back a little way. The formal calculation of tho oib.ts or binaries was first attempted > fio French astronomer, Savary, m Hcrscnel first registered in 18d « bright pair in tho constellation or the Greater Bear. Since then it .has gone through two complete revolutions, and it Has approximately conformed to tho orbit charted by the 'Frenchman. He thus (incited a new line of inquiry, it is not free from difficulties. ltmruxMimal errors may introduce material inaccuracies into tho diagrams representing their revolutions. Only a portion of “tho orbit can be “ plotted at any particular time, and it is bard sometimes it is impossible—to complete an ellipse from a single section, even a that section be of considerable extent. A star mjay thus deviate widely from its predicted successive places.. All such* deviations apply to star binaries. Only fifty have had their paths accurately calculated. Only forty visual 1 pairs with periods of 100 years have been found to traverse their, assigned orbits. Few with longer permcis have had their orbits reliably computed. Such is the work of ninety years m this ! ‘ nC ' THEIR SYSTEMS. ‘ Hero we need look for the. sin‘n.icity so often ascribed to Naane, which is infinitely various. Each pair has a system of its own. -Its lustoij,.dynamical relations, and physical state ■afford abundant materials mr .study. “The superb southern binary. . the star Alpna in the constellation ot tho Contour, our nearest • neighbour n space, was discovered at Pondicnery in 1(389 by tho Jesuit father Lictuud (another Jesuit was the first to suggest in 1777 that pairs of stars were -genuine couples). Since then it nas accomplished two complete revolutions and* is midway through a third. Hs period is eighty-one years. Its or Jit is £ n elongated ellipse. The distance of tho two stars from one another is a speciallv important datum. On it depend both the mass and the velocity. At their point of closest mutual npproac. they are separated by a space slightly exceeding the distance between Sr.-urn and the sun; forty years la cer the gap enlarges to far beyond the distance or NcptuneC Each star is abouir to our sun in bulk. Their masses boincr virtually the same, their reciprocal o-ravitating nower is nearly the same. Their orbits are similar as well anconal. Together they slacken in speed and accelerate together. . Their movements are equal and opposite. Him ot trio stars sends forth fully thrice the light or its companion. Tho. dimmer star is also tho. Yellower. Me may safely affirm that the two were contemporaneous in origin and arc closely alike m chemical composition. Both are of t he solar type, and Sir David Gnl has singled out the chief star as a model ot our sun. It is indeed reasonably certain that the more luminous is just such another sun as sensibly warms our bodies this mid-wiinter afternoon. It is possible that the great binary has other dark or bright companions, o* which, three or four were located* in igep. it will he the task of observers of these southern skies to decide. They must be no-Juminous. or rathe: they reflect the Ivi't. of their suns, out that dor- net diminish their importance. Our earth and all the planets are ligated by the sun. AN AMERICAN AMATEUR. Mr S. W. Burnham was a shorthand writer in Chicago when Alvau Clark, tho discoverer of tha companion oi Sirius ■ seven years before, returned from observing the lowa eclipse oi August 7, 1869. Encouraged by the cluer man, Burnham constructed a six-inch refractor and entered on a career of discovery. He devoted himself specially to double stars. In lui3 he. issued his first catalogue ol stars, and it contained eighty-one new pairs. His catalogue of the year 1900 comprises 1,990 binaries, discovered between 1871 and 1899. Attached to tho Yerkes Observatory, he has used some of the largest and finest instruments in the world—tho thirty-six-inch on Mount Hamilton and the incomparable forty-inch at Yerkes. Of the total entries, 133 record the .further analysis of pairs. As he himielf says, more than one-tenth of the cntrfcs “.is made up of previouslyknown doubles, where- ono of tho components has been again divided, or a much 'nearer star has been added to the system.” In this way not "only resin doubles, but triple and quadruple combinations have been disclosed. These are very various, but a coupled arrangement appears to prevail. Not only doubles revolve round one another, but two pairs revolve round one another. Or a close pair plays the part of satellite to a single star, or “a single star circuits a duplex primary.”. Everywhere there are wheels within wheels. So far back as 1779 Her sell ol registered epsilon Lyras as a “ double double star.” Each of two stars (visible to sharp eyes) is found by telescope to _ be compound. So in a V.tar of Scgrpion, where the original division was effected bv Hcrschel in 1752: In 1816, at Cincinnati), the companion-star split un under Mitchell's scrutiny, and in 1874 tho primary star was decomposed by Burnham—the two into “beautiful close pairs.” They are now perceived to form ono vast quadruple system. STAR-DRIFT. There is a remarkable case of stardrift in the constellation Pegasus, where kappa (a star of tho fourth magnitude) was found by Struve in 1828 tc have a faint attendant. In 1880 Burnham divided the primary into “ an excessively close couple,” with a period of only 11.4 years, almost the shortest period of any binary within telescopic range. The . faint companion discernod by Struve travels with the system and must bo attached to it. lint how such small stars, with but. little gravity, arc tewed .along like a boat bv a ‘ steamer, remains a mystery. Such cases present, many curious and far-reaching problems. ■_ Another ease of drift is still more remarkable. Here four stars or two pairs of binaries are swept along by a ,-wift current that is narrow between +’ho nrimovies and 118 times wider, tho •van amounting to some billions M miles, bo tv.-con the . secondaries. Sir .John Herschel discovered the.clientstar of the first pair in 1834, and B. T. A. fanes, of the Observatory at the Cape, discovered the other ‘ neat pair ” before 1899. SYSTEMS' OF BINARIES. Ono of the most successful discoverers of stellar systems is Dr T. J. See, of the United States, and -a graduate in Astrofiomy of Beilin. In he discovered no fewer than oOOdouble stars and was struck with the dullness of lustre in their satellites. Ono ot i the least expected characters is t.ie rrequont inclusion of dusky or even wholly obscure members. The German astronomer, Bessel, was the first to perceive a lack of uniformity in tho m'oper motions of Sirius and Procyon. Both greater and lessor stars pursue undulating tracks across tho sky, swaying from side to side as if pulled by an accompanying attractive mass, and ho predicted, eighty years ago,

that these radiant luminaries would piove to be binaries. Not till Alvan Olarlc discovered it in 1862 was the companion of Sirius found. But it is faint beside its blazing primary, which gives forth tho light of twenty-one suns, while the, secondary emits only one1700th part of the solar luminosity. Like the satellite of Procyon, it is drifting towards extinction. OTHER SYSTEMS. In the star seta of the constellation Cancer two brilliant stars revolve round one another in sixty years, and at six times their mean distance they are attended by another pair, bright and dark respectively, which circle round one another in eighteen year's, and circle round the primary pair in a. leisurely revolution of perlwips seven centuries. Tho dark star gives rise to abundant speculation. la it a lingo planet crowded with an innumerable population wit bin its capacious boundaries and enjoying a genial climate that is maintained by the, constant presence of three vivid suns? A CORRECTION. A correction of some importance can now bo made. Mr Ait ken, of the-Lick Observatory, in 19G0 found that the components of ono of Otto Struve’s double stars wore separated by a comparatively slight distance, instead of thrice that distance. Hussey accordingly revised their elements and halved tho period, now fixed at 5.7 years. This is the shortest of the telescopically known periods. An we shall see, others still are shorter. SPECTROSCOPIC) BINARIES. (Tho old astronomy has shewn its vitality by accepting the new methods placed at its disposal by the spectrum. The discovery of spectroscopic binaries has added immensely to the resources of the traditional astronomy. The principle on which it rests—that spectroscopic binaries “are revealed by tho. periodical motion-shifts of their •spectral lines”—was-.first applied to the ascertainment of the radial movements of the stars by .Sir W. Huggins in 1868. ‘ Since then tho number and rarity of bo system brought to the astronomer’s knowledge are, amazing, Three score pairs were discovered in the first thirteen years. The first star spectroscopically divided was M : zar, the middle “ Horse ” of the Plough, which was besides a telescopic binary. Alcor. the “’Rider” of tho “Horse” “drifts with it and venders it a quaternary combination of enormous span and incalculable period." M. Flammavion believes that nearly 18,(100 years will ellipse before they have completed their circuit. The twinkle of Alcor, barely visible in the Middle Ages, is now ap-. ptoo'nblv brighter. Miss Maury, examining the Harvard plates, discovered the spectroscopic irnary/beta "in Auriga. In tbe plates she saw two brilliant globes that give together tbe light of twenty-eight stand-ml suns, and circuit in four days. Is Ibis, at- last, with Spies, of the Zod?rcM Virgin, the shortest binary period? No. 50T,,0o T,, 0- of tho very rapid Avgol varieties finish a circuit in loss than a- day. TRIPLETS AND QUADRUPLETS. To a telescopic triple." star the “ I'lappa” in the ccnsteliintion Pegasus, the spectrum has added a. fourth component. A pair of Burnham's was found by Campbell in 1900 to be closely associated to a dark attendant. Another binary, in tho Greater Boar, was ip tire same year decomposed by Wright into a ternary combination, A third member was. annexed to ilfe “stately system ” of Castor by Belopolsky in 1896; or, rather, it was a fourth, since a cm nil remote star had previously been found to keep paco with the lustrous a:jd illustrious pair. The qimcrnity opens up a field far fresh and important inquiry. DUPLICITY 0-F A SUN. A still grander discovery was that of the duplicity of C'apella, which is acknowledged to be the premier star in lho Northern Hemisphere. In 1899 Director Campbell and )Ir Newall independently identified it as composed of two brilliant orbs, with n velocity of 86 miles a second, and circuiting one another in a period of 104 days. The two toe-ether have a luminous output of more than 100 times the luminosity of our sun. The joint mass of tiro couple is onlv seventeen times that of the sun. It is therefore, like the giant suns of space, comparatively tenuous in composition.