CHEMISTRY OF THE STARS

Taranaki Daily News, 24 November 1926, Page 12

CHEMISTRY OF THE STARS

THE MAGIC PRISMS. AN INTERESTING LECTURE. Last week at the weekly meeting of the Hawera Astronomical .Society a most interesting paper was given by Mr. L. W. Holmes on the chemistry of the stars. Mr. Townsend presided over a fair attendance of members. The usual discussion took place after the paper was read, when Mr. Holmes was accorded a hearty vote of thanks for his interesting discourse. The following is an abstract of the subject:— Sir Isaac Newton made the initial discovery that the light of the sun consists of rays differently coloured and differently refrangible, but for more than a century after no one suspected the intricate detail involved in this broad statement, till in 1802 Wollaston remarked that the spectrum given by sunlight analysed in a prism was really crossed by many fine dark lines. Later, Fraunhofer, the optician, found these dark lines to be invariable in their relative positions, and carefully mapped their places, giving to the most distinct ones the letters by which we still call them. L. Foucault in 1849 set himself to study the origin of these lines. He tried to supply the deficiency of the D-line (in the yellow) by passing sunlight through a source of yellow light (an electric arc), but found the dark line in question much darker than before. He was led to the discovery that glowing vapours absorb from a brighter light passing through them the very colours which they themselves emit. Three years later G. Stokes showed that the D-line was caused by sodium, and in 1859-60 R. Bunsen and G. Kirchoff added their own discoveries to what was already known, and established spec-trum-analysis as a science. They showed that every element gives its own characteristic line or lines in the spectrum—bright lines by direct radiation, dark lines by absorption of transmitted light. They showed that when light from any source gives known lines in its spectrum, then we can infer the presence of those known substances in the source of that light. Elements give spectra containing fine lines; the spectra of compounds of broad-shaded bands. These discoveries have been of much use to chemistry on the earth. By the spectroscope many pew elements have been discovered; two new alkali metals by Bunsen and Kirchoff themselves; and later, gallium, indium and thallium among others. Spectroscopy has also been very important in the .study of the radium elements. But for the chemistry of the outer universe it is all-’impor-tant; we can find out nothing about the composition of the stars but by the peculiarities of their light. Prominent among the workers in astronomical chemistry have been Leckyer, who discovered helium in the sun thirty years before it was found on earth, and Huggins, who first used a method for measuring the exact position of stellar spectrum lines, and who published an “Atlas of Stellar Spectra.” We find, from a study of the composition of the stars, that matter throughout the universe is, on the whole, the same, and seems to have been created in the same manner. We can identify with earthly elements almost all lines we find in the spectra of heavenly bodies. Nebulae, the most primitive rudimentary forms of matter, show only our two lightest elements, hydrogen, and helium, and sometimes not even them; but always a single green ray from an elements we do not know on earth — “nebulium.” The hottest “gaseous” stars show little else but hydrogen and helium, though many have traces of such elements as the sun contains. Our sun belongs to the next coolest type of star—its spectrum is ruled across from end to end with lines belonging to most of our commoner and lighter earthly elements. Sodium, calcium, magnesium, titanium and iron may be mentioned as abundant. Cooler again are red stars like Betelgeuse and Antares, whose spectra show in addition dark bands traced to titanium oxide, the first instance of chemical combination. The coolest and dimmest stars show by their light that carbon compounds occur in their atmospherics. In addition they give bright lines of nitrogen, hydrogen and oxygen. New stars or novae go through, in their life of weeks or months, a cycle of all the above changes, showing in many eases the lines doubled (two bodies taking part). This, though it does not explain everything, is the most important clue we have to the causes and progressive changes of these phenomenal outbursts. Our earth docs not exactly follow the composition of the sun. Oxygen (our most abundant element) and potassium (a common one) are only rare on the sun, if they exist at all. So the earth does not seem to have been formed entirely from the sun. There are many other such facts and problems which ‘the magic-prism” open up to us. Science has shown us many a marvel in creation, but there is surely none more wonderful than this: We van examine a ray of starlight aud say “I know' whether it is solid, or gas, or both; whether it is coming or going, and how fast, how hot it is, and exactly what it is made of.”