GREAT CLUSTERS OF STARS IN THE MILKY WAY

Wanganui Chronicle, 25 February 1947, Page 7

GREAT CLUSTERS OF STARS IN THE MILKY WAY

(By “Sky Pilot") The planet Saturn, a beautiful object some 886,000,000 miles from the sun, we considered last week. This present article deals with an aspect of the great system in which Saturn is contained, but in which it would never be seen from the nearest star to the sun. This is the Galactic or Milky Way system which Herschel, the great astronomer, determined to be lenticular in shape—circular, flat, and many times wider from edge to edge than thick from top to bottom. He considered its diameter to be 6000 light years but photographic studies reveal it to be 100,000 light years, with a thickness of 10,000 light years. The famous Harvard astronomer, Harlow Shapley, showed that the galactic centre lies in the direction of the constellation of Sagittarius, 33.000 light years distant, and coincides with the centre of the system of globular star clusters. Herschel also showed that the sun and its family is a member of the system, and it is now determined that we are well over halfway from the centre of the edge. The sun, planets, comets, meteors, stars, star clusters, and nebulae belong to the galactic system. “Our vast system consists of 30 to 100 thousand million stars, spinning on its centre like a gigantic starry pin-wheel with terrific rapidity. At the sun’s distance from the centre, one rotation is completed in a trifle over 200 million years, the sun and the earth being carried round the nucleus at 200 miles per second.” And our galactic system is only one of millions of such systems in the great universe. “RIVER OF PEARLY LIGHT”

The backbone of the galactic system is “the river of pearly light, the Milky Way." In Greek mythology it represented “the path scorched by the chariot of the sun when Phaeton ambitiously attempted to drive Apollo’s fiery steeds but allowed them to get beyond his control." It is also said by the Greeks to represent the dust stirred up by Perseus in his haste to rescue Andromeda. Primitive peoples of many lands have had legends about the Milky Way. American Indians, Eskimos, and African bushmen called it the Ashen Path, so that benighted travellers might easily find their way home. The Greek Democritus believed that the Milky 'Way was composed of swarms of stars unseeable with the naked eye because of their faintness. Two thousand years later telescopes of large size have proved this to be the case. Galileo was the first with his small telescope to observe that the misty pathway is really composed of numbers of stars. More powerful telescopes have shown that the seem-

ing nebulous texture and mysterious softness of the Milky Way’s light rays from millions of distant stars. The spectroscope reveals an endless variety of these suns differing in size, density, luminosity, surface temperatures, and physical conditions. GREAT STAR CLUSTERS Great star clouds such as in Sagittarius and Aquila show immense piling up of stars, whilst also hidden within it are nebulae and open and globular clusters. The luminous background, so faint that moon-light and city lights cause it to fade, is only partially seen a any time, portion of it being below the horizon. Actually it forms a complete and continuous belt and is, as it were, the plane of our great galaxy. Its central line cuts the celestial equator about 60 degrees, therefore accounting for its great varying position in the heavens with the hour of night and the seasons of the year. Sometimes the Milky Way is seen lying on the horizon and at times above our heads, and all places between. Its average width is about 20 degrees. Located in Cepheus and Cassiopeia in the Northern Hemisphere, it is about 20 degrees wide and has an irregular outline in Auriga and Taurus, and narrows near Orion to 5 degrees but widens as it crosses the equator in Monceros. In the Southern Hemisphere dark lines divide it as it continues through Puppis, Pyxis and Vela (names of constellations) to reach maximum southerly declination in Crux and Musca. THE COALSACK VOID Lying between Crux and the Pointers is the dark oval of the Coalsack amidst the Milky Way. Then heading northwestwards it passes through Circinus, Lupus and Norma on to Scorpio and Sagittarius; and in Ophiucus, the Milky Way is divided and continues so through Serpens, Aquila, Sagitta and Cygnus. In the latter it seams to have split into two branches separated by a long dark island. These apparent splits are considered to be great dark dust clouds possibly obscuring areas equivalent to the brilliant areas of the Milky Way that we see. The richest parts of the stream are those in Sagittarius and about the Southern Cross. Here the milky, cloudy patches resolve themselves through the powerful telescope into beautiful clusters of stars of many colours and mysterious nebulae and charming open clusters and globular clusters. The Vela-Crux region is magnificent and is another of the glories of the southern hemisphere which should be viewed through the telescope whilst this portion of the sky is visible.