IN STARRY SKIES

Evening Post, Volume CXII, Issue 123, 20 November 1931, Page 16

IN STARRY SKIES

itfHE DOLPHIN, THE LITTLE 1 HORSE, AND THE LYRE

(By "Omega Centauri.")

t This map completes our survey of 1 all the constellations north of the equator that are visible to us. It affords an excellent example of tho strange way in which the constellation figures are jumbled together. In the south-west, the top left-hand corner ive see a portion of the interlaced figures of Serpens and Ophinchus. Tho rest of the top is filled by the Eagle, and a large area in tho north-west by I he Swan. Below tho Eagle is tho Arrow, and beside it the Dolphiu and tho Little Hoiso. which are grotesquely small in comparison with it. Hercules guards the west margin, and Pegasus appears on the cast. Between Hercules and the Swan is tho Lyre, a beautiful little constellation strangoly placed among living creatures. Directly south of the Swan is the Fox. All these, except the last, are very ancient constellations, and were given by Ptolemy in his Almagest. The Fox and the Goose, Vulpecula ct Anscr, was added by Hevelius in 1690. The Gooso Tias since disappeared, but the Fox survives. Although these constellations form such an ill-assorted group, the

names are indispensable in becoming familiar with the heavens.

Our solar system, we have seen, lies in a large star cloud which forms one of the outlying members of the supergalaxy. Looking out into space we see stars in all directions, but the dominating feature of the whole arrangement is the Milky Way, a vast assembly of star clouds or galaxies arranged in a greatly flattened form, which we view from within. To represent what we see on a flat surface is a difficult problem. Though scattered in all directions in space, the stars appear to us as if they were placed on the inside surface of a vast hollow sphere. Now a sphere surface cannot be reproduced on a plane without distortion. If a small portion only of the sphere is represented this is not serions. Each point can then be projected onto a plane as it would appear to_ an eye placed in some assigned position. But if a whole hemisphere is shown the distortion must be considerable. For this reason maps of all tho stars visible at one time are used chiefly as index maps, and individual constellations are represented separately or in groups on s, larger scale. But if one constellation only were given in each map we should need quite a large star, atlas. Ptolemy enumerated 48 constellations, and 66 nave been added since. Fortunately " a number of the modern ones are no

longer recognised. But what are these constellations? Are they physically connected systems, or merely chance groupings? There are some of each kind. In looking at the sky on a clear night the eye immediately picks out many striking groups, but the points of light in each are too few and too isolated to present any clear picture of forms or objects. It is easy to see faces in the fire, or to notice suggestions of figures and other objects in the markings on the moon. But in spite of the greater difficulty the ancient observers, with their vivid imaginations, peopled the heavens with heroes, animals, and inanimate objects, and we still use the names they gave. One lady is said to have remarked that she could easily understand how astronomers find out what stars are made of, and how far off they are, but she couldn't imagine how.ever they managed to find out their names. Well, accepting the names given by ancient astronomers, it is found that in several striking cases the stars so associated form real physical systems. All but one of the bright stars of the Great Bear, for instance, are moving

together through space. The Hyarles, except AldCbaran, arc. also travelling together dn parallel patlis. They form part of Hie Taurus group which is known to contain about 80 stars. Most of the bright stars of Orion form another associated group, now 500 light years from us and moving almost directly away at the rate of twelve or thirteen miles per second. Of the fifteen brightest stars in Scorpio, ten, including An tares, are moving together. JEpsilon, Zeta, and Kta have widely divergent motions and do not belong to the group, which, however, contains Beta Centauri and Bpica, as well as other stars in Ocntnurus, Crux, and Virgo. Amongst other well-known moving clusters are thoso of Perseus, Sagittarius, and Vela. In contradistinction to those, the Great Dog, Cassiopeia, Aquila, and Lyra are merely chance distributions. That is they consist of stars at widely different distances from us moving in diverse directions, and they appear to be associated simply because at present they lie in nearly the same direction from us. In reviewing the constellations we glanced first at those lying along the bright stream o£ the Milky Way. Next we studied all between tho celestial equator and 50 degrees-north declination. These appear with tho north ut tho bottom as they cross the meridian. We have still to show those that lio between, the equator and 50 degrees south. These, when on tho meridian; extend from an altitude of 49 degrees up to well past the zenith. They appear tilted towards the left as they rise and towards the right as they set.

Some of the constellations shown to-

day were described when discussing tho Milky Way, which passes from the Eagle through the- Arrow and tho Fox, into the Swan. Tho Lyre lies just on the west side of the stream and the Dolphin and the Little Horse on the east of it.

Lyra represents the Celestial Harp presented to Orpheus by Apollo. It is marked chiefly by the brilliant star Vega. This is easily found, as the three chief stars of the Eagle point almost directly towards it. Vega is the brightest star in the Northern Hemisphere and ia surpassed only by the three southern stars, Sirius, Canopus, and Alpha Centauri. It owes its distinction largely to the fact that it is one of the nearest stars. Its distance is only 26 light years. Though fifty times as brilliant as our sun it is outshone by GaiiopusSsti.biJt' sixteen hundred times. Beta Lyrae is a far brighter sun than Vega, but is more than a hundred times as far away. The most interesting objects in Lyra are M 56 and M 57. The former is a globular cluster estimated to be 80,000 light years away, the latter is tho celebrated Ring Nebula which has already been fully described. Delphinus, the Dolphin, was known to the Greeks as the Sacred Fish. The Hindus called it the Porpoise. Ovid took the constellation to represent Ainphitrite, the goddess of the sea, and wife of Poseidon. In some stories the Dolphin is said to have been placed amongst the stars as a reward far having, found Amphitritc when she fled from Poseidon to the uttermost parts of the sea. The stars of the Dolphin make a pretty little group to the east of the Eagle. Beta is an interesting system, a close binary with a more distant companion. The luminosity of the system is about 140 times that of the sun. Gamma is a binary. Alpha, Beta, and Gamma are all approaching us, but at different rates. HlO3 and 6905 are nebulae; Equuleus, the Little Horse, was sometimes called the first horse, as it rises before Pegasus. The Arabs called it "Part of a Horse," and the Hindus "the horseman." Delta is a binary with one of the shortest periods known, 5.7 years. It is 46 light years away. Gamma is a binary ten times as far off, and Epsilon is a triple star. The main binary was discovered by Strove in 1835. The orbit, almost edge on to us, appears such a narrow ellipse that sometimes the binary character cannot be detected even with the laTgest telescope. The period is 97.4 years.