FLIGHT OF THE STARS

Taranaki Daily News, 5 October 1929, Page 17 (Supplement)

FLIGHT OF THE STARS

MOTION TOWARDS VEGA

(By

Rev. B. Dudley,

F.R.A.S.)

Nothing seems more certain to visual observation than that the stars (apart from the planets which belong to the solar system) maintain ever the same relation to each other, that they are fixed points in the vault of heaven. Night after night, generation after generation, the unassisted eye detects no change in their grouping and configuration/ To the more critical eyes of instrumental observation, however, nothing is surer than that in the heaven's, as in the earth, -everything changes. The stars move “in their courses” in a sense not understood by the ancients. Thenmotion appears to us to be so small only because they are so very far off. Our sun is a star rather less in size and intrinsic brightness than the average; and, like all the others, is journeying rapidly through space. Blearing his retinue of planets, comets, meteors, etc,, including the earth with its teeming population, he is, at a speed of 12 1 /™ miles a second, travelling—falling, one may as correctly say—towards a known region of the heavens, although the ultimate destination is unknown.

The first astronomer to suspect this movement, known as the .“proper motion” of the stars, was Edmund Halley, a Contemporary of Newton, and Royal Astronomer from 1719 to 1742. He detected evidence of such motion in Arcturus, Sirius and other stars. From New Zealand .Arcturus can be seen brightly glittering in the northern skies. During the present month (October, at 6 pan.) it will be found a little distance west of due north and low down on the horizon in the constellation Bootes, Since the time of Hipparchus (146-126, 8.C.) Arcturus has shifted among the. stars, of that constellation across a distance equal to 2 1 /a times the diameter of the full moon. During the same period Sirius has moved a distance equal to 11/,I 1 /, times the lunar diameter. These are, of course, only the apparent movements of the stars named —their “angular motions,” to use the appropriate technical term. The real distance in space over which these bodies have travelled is a very different story. Arcturus, for example, is known to be speeding on its pathway at the velocity of 2SB miles a second. "Since Hipparchus measured -its position, it has travelled approximately. 18 million million (IS billion) miles, but being so far away, its apparent motion in that period is, ,as already stated, only 2% times the moon’s diameter. The swiftest known (Barnard’s Runaway Star, as it is called, after the discoverer) passes over a space in the heavens equal to the moon’s diameter in ISO years. The vast majority of the stars move much more slowly than. Arcturus, Sirius, Alpha of the Centaur, Vega and their few compeers in the matter of .speed. The. proper motions of thousands of stars are known with varying degrees of certainty. They are flying throug’h space, singly,- in pairs, in groups, clusters, and swarms, or in vast streams of unimaginable magnitude.

Our own star, the sun which is the light, fire and life of the earth, i$ a slowgoing traveller, for, while the average speed of the . distant suns is about 20 miles (20.2- to be exact), our luminary carries us with it on its endless journey at the more leisurely speed mentioned.. Professor Kapteyn thought it might be 15 miles a second, or nearly 500 million miles a year, but the general estimate among astronomers in favour of the. lower speed, which works out at rather more than a .million miles a day, or 367 million a year. As a result of his painstaking observations and calculations at the Lick Observatory, Dr. W. W. Campbell has been able to announce among other interesting things the most surprising fact that the older a star is the quickei\it moves. There are suggestions and inferences derivable from this unexpected discovery, but no completely satisfactory explanation. It is not yet proved whether the path of the sun is a straight line or a curve, but at the present time it is moving towards a point in the heavens not far from the bright star Vega in the constallation Lyra, also visible at the present time from New Zealand—very low down on the northern horizon, and some distance east of Arcturus. At . the opposite side of the.heavens is found Sirius, not at present .in ; our. night skies. The entire solar system, a tiny dot ,on the page' ,of/the 'universe, is making its flight from a point near this extremely brilliant star. Vega is itself moving towards us at. a rate comparable with that of the sun’s velocity towards him. which means that to-night we are nearer to him by something like two millions miles than we were last night. As, however, Vega is distant from us about 30 lightyears (30 times the distance light shoots through space in a year at a velocity of many thousands of miles a second) the two bodies will not meet to-morrow. Moreover, as Vega and the sun pass each other the distance between them is likely to be so great that there could be no inconvenient results. This for the population of the earth is reassuring, since Vega is an enormous sun over 100 times brighter than our own! How much hotter he is it would be hard to say!

There are many complications in the problem of determining star distances and motions which require expert treatment and cannot be referred to here. There is, however, one fact simple enough for the average reader’s understanding that shall.he mentioned. It may be stated ,as follows: If a man walks through a forest of tall trees, the trunks in front of' him will appear to open out and grow taller at a rate determined by the speed with which he himself is moving, while those exactly behind him will appear to close in at the same rate. Those on either side will exhibit an apparent backward shift. The like apparent motions characterise the stars, and the lines of direction diverge from Vega “in front” of us, converge bn Sirius behind. That is to say, these two stars aro the respective vanishing points. As might be expected; the nearer'stars show the greatest amount of shift, just as in the forest the trees in the foreground of the advancing observer appear to open out in front,'close in behind and drift backward on either side at' a greater rate than the remoter frees.