"CREAM" OF THE MILKY WAY

Rotorua Morning Post, Issue 5324, 10 February 1947, Page 3

"CREAM" OF THE MILKY WAY

GALAXY FHOTGGRAPHED ASTRON OMICAL ACHIEVEMENT OF DR. BAADE Astronomers at last have seen and photographed what they believe to be a part of the centre or nucleus of the Milky „ Way, or galaxy of stars, of which the earth is part. It is a d'ense clcud of faint stars in the southern sky 172 .quadrillion miles from the earth and hundreds of biliions of miles in diameter. In spite of its size, the photographed ' part of the star cloud occupies less sky area than the moon as seen from the earth. This astronomieal achievement by Dr. W. Baade, of Mt. Wilson Observatory, San Franeiseo, further strengthens the already widely held belief that the form of the Milky Way is "something like the mainspring of a clock, with an upward bulge in the middle. Dr. Baade veported his work in the publication of the Astronomieal Society of the Paeific. Whethei- people on earth ever would be able to see the Milky Wiay nucleus was a question along with the rest of the solar system, is well buried in the Milky Way, and because of this it is difficult to loolc into outev spaee in eertain directions. To visuali.se the earth's position, ' conssider Ihe galaxy to be roughly | the shape of a noeket watch. The ; sun and its planets would constiture ! an insignilicant speck about oue-third ! the distance irnvard from the rim of 'i such an iinaginavy watch — toward the | shaft which drives the hands, and : somewhat helow the surface of the i face. To see The centre of the watch, j a speetator on the insignificant speck ■ world have to look through several I working parts of the watch; and to f see the galactic centre an earth dwel- , ler would have to look through an cn- ; ormous amonnt pi' intervening eosmic j mi'iitev. i For the same reason, it is comparatively easy for earth dwellers to see other galaxies, centres and all, far i outside the Milky Way. They only j have to look through the thinnest part j of the imaginary watch, towards its face or back, thus encountering a minimum (of interferer?ee from mr.fter j within the Milky Way. From observing these other galaxies astronomers had formed ideas j abcut the Milky Way centre. Fome of the far distant galaxies had raised centres composed of a peeuliar kind of stars. Ahundant among them j weve the so-called cluster variable, i stars whose light fluctuates in a char- i acteristic manner. j On the theory that our own Milky ! Way centre might be raised sufficient- j ly to be seen above the main mass of * eosmic material, Dr. Baade pointed j Mt. Wilson's ilOO-inch reflecting tele- t seope, at present the world's largest instrument of its kind, at the bright i cloud in the constellation Sagittar- , irs. which in summer c-an be seen i from the United States low in the j scuth or south-west sky. He chose i that cloud because it was in the ■ righfc direction, and liecause he knew j it was a dense collection of stars j something like those in*the nuclei of ; other galaxies. ; Centring on a glooular star cluster j known as XGC 6522, Dr. Baade photo- j graphed a little more than one-third of a square degree of sky, a spot ' somewliat smaller than the apparent ; size of the moon. The picmres oi ; that little spot disclosed 152 variable ; stars. 30 limcs as many as are found 1 in eoviesponding' areas of the outer ; porlioii.s of the Milky Way. Dr. Baade caiculated the distance of NGS 6522, the key ohject in Ihe j cloud at ncarly 30,400 light-years. _ A light-year, the distance which ; light will travel in a twelve-monlh, ; is six million million miles. .This , distance for the galactic centre tvas j in line uith computations previously made by Dr. Harlow Shapley, | of Harvard Univevsily from data of !1 dilforenf kind. D.\ Baade concluded, iherefove, that J sincp the hright colour in Sagittarius 1 is composed of stars characteristic of j Ihe centres of other siinilar galaxies. j atul since it lies at tho expected dis- ] tance from the earth, it must be part j

of the huh which rises above the main i galavtic mass. "Moi'eover," he added, "it nov ap- j pears probable that* the faint corona j of stars surrounding our galaxy ( represents a continuation of the gal- j actic bulge." j