For our explanation, we must go back to a classical experiment made by Sir Isaac Newton. He proved that white light, when made to pass through a glass prism, is split up into a variety of colors. There are seven primary colors, constituting the visible spectrum. These are red, orange, yellow, green, blue, indigo and violet. We now know that there are both “ultra-violet” and “infra-red” rays, invisible to the eye, above and below the spectrum, but this was not known until long after. The essential fact is that light, when passed through a prism, is split up into its primary colors.
THE SPECTROSCOPE
The instruments employed were necessarily soon refined, and the modern “spectroscope” resulted,—a piece of apparatus of great delicacy, capable of studying these effects with exactitude.
The function of the spectroscope is to receive a sample of light and to separate its different components. In a broad sense, everything that can be seen has a spectrum—flame, blue sky, red hot metal, the sun, the electric spark, etc. We can at once divide these things into two classes, (1) those that are visible because they emit light of their own; (2) those that can be seen only by virtue of their reflecting, diffusing or transmitting light that falls upon them from other sources. The former are called “emission spectra” and the latter “absorption spectra.”
Now, when practically any spectrum be examined in this way, it will be seen that certain bands of shadow, or dark lines, cut across the light spectrum, in absorption spectra, these are the things which are studied. Thus, when we observe the spectrum of the sun, or of many of the stars, we find that the spectrum may be described as a continuous spectrum, from which a number of narrow lines are omitted. The lines consequently appear dark on a bright ground. These are called “absorption lines.”
Just why these dark lines appear would take us too far afield to explain here; suffice it to say that every chemical element has been found to yield a different spectrum; that is to say, the number and arrangement of these dark lines will indicate the presence of the element in question. Whenever certain lines appear on the spectrum, we may be sure that such-and-such an element is present. Thus, Kirchhoff first proved that two of these dark lines were caused by the white light of the solar photosphere having suffered absorption at the sun, by passing through a stratum of glowing sodium vapor. Sodium was thus shown to be present in the sun. Other elements were similarly identified, not only in the sun, but in the millions of stars in the heavens. By means of spectrum analysis, therefore, it has been possible to detect and identify the various chemical elements present in any given sun or star in space.
ASTRO-PHYSICS AND CHEMISTRY
In this manner, about forty terrestrial elements have been shown to exist in the sun. Carbon, oxygen, iron, silicon, nickel, etc., exist in the sun just as they do on our earth. On the other hand, many elements, such as mercury, nitrogen, sulphur, and boron do not appear, although they are found in abundance on the earth. Yet several elements were shown to exist in the sun which up to that time had not been discovered here. Helium is an example. (From the Greek, Helios, the Sun). And yet, when attention was directed to this element, it was soon found in our earth, and is today so common that helium gas is employed to inflate balloons, in preference to hydrogen, on account of its non-combustibility.
SPECTRUM ANALYSIS
Spectrum analysis, then, tells us the precise chemical constitution of the various suns, or stars, in space, and it also tells us that these stars are incapable of supporting life such as we know it. As Dr. E. Walter Maunder says, in his book, “Are the Planets Inhabited?”: