The Progress of the Century

by Unknown

Before the introduction of spectrum analysis all stars were supposed to be suns, and the only difference recognized among them was one of brilliancy and the variation of brilliancy in the case of some of them.

It ultimately came out that great classes might be recognized by the differences of their spectra, which were ultimately traced to differences in their chemistry and in their temperature, as determined by the extension of the spectra in the ultra-violet, the whiter stars being hotter than the red ones, as a white-hot poker is hotter than a red-hot poker.

Next there was evidence to show that a large proportion of the stars were not stars at all like the sun, but swarms of meteorites; and in this way the mysterious new stars which appear from time to time in the heavens, and a large number of variable stars, were explained as arising from collisions among such swarms.

The inquiry which dealt with the spectroscopic results, having thus introduced the ideas of meteor swarms and collisions to explain many stellar phenomena, went further and showed that the various chemical changes observed in passing from star to star might also be explained by supposing the whole stellar constitution to arise from cool meteoritic swarms represented by nebulæ, the changes up to a certain point being explained by a rise of temperature due to condensation towards a centre. Here the new view was opposed to that of Laplace, advanced during the last century, that the stars were produced by condensation and cooling; but Kelvin had shown, before the new view was enunciated, that Laplace’s view was contrary to thermodynamics, a branch of science which had developed since Laplace published his famous Exposition du Système du Monde.

After all the meteorites in the parent swarm had been condensed into the central gaseous mass, that mass had to cool. So that we had in the heavens not only stars more or less meteoritic in structure, of rising temperature, but stars chiefly gaseous, of falling temperature. It was obvious that representatives of both these classes of stars might have nearly the same mean effective temperature, and therefore more or less the same spectrum. A minute inquiry entirely justified these conclusions.

So far had the detailed chemistry of the stars been carried in the latter years of the century that the question of stellar evolution gave rise to that of inorganic evolution generally, the sequence in the phenomena of which can only be studied in the stars, for laboratory work without stint has shown that in them we have celestial furnaces, the heat of which transcends that of our most powerful electric sparks. In this way astronomy is paying the debt she owes to chemistry.

THE SUN AND HIS SYSTEM

Although the outer confines of space have, as we have seen, been compelled to bring their tribute of new knowledge by means of the penetrating power possessed by modern telescopes, and the cameras and spectroscopes attached to them, the study of the near has by no means been neglected, and for the reason that in astronomy especially we must content ourselves in the case of the more distant bodies by surmising what happens in them from the facts gathered in the region where alone detailed observations are possible.

Thus what we can learn about the sun helps to explain what we discern much more dimly in the case of stars; a study of the moon’s face we are compelled to take as showing us the possibilities relating to the surface condition of other satellites so far removed from us that they only appear as points of light.

To begin, then, with the sun. Where a volume might be written, a few words must suffice. I have already stated that at the beginning of the nineteenth century the prevailing opinion was that it was a habitable globe. It was limited to the fiery ball we see. At the end of the century it is a body of the fiercest heat, and the ball we see is only a central portion of a huge and terribly interesting mechanism, the outer portions of which heave and throb every eleven years. Spots, prominences, corona, everything feels this throbbing.