Similarly on 8 June 1919 a brilliant new star appeared in Aquila, almost on the border between Aquila and Serpens. When brightest this was almost as bright as Vega, the brightest star of the northern heavens, and it was of a very blue color. It rapidly faded away, until now it is onl' a telescopic object.
By what convulsion of nature these objects burst forth it is quite beyond the power of our present science to decide. It is certain that the amount of light and heat emitted by these stars was suddenly increased hundreds or even thousands of times. One of the most plausible explanations is that of a collision. It is supposed that the star itself may have col lided with another—perhaps a planet in its neighborhood— or rushed to its own destruc tion in some nebulous mass. But this is only conjecture.
Very curious has been the fate of these objects after they have faded away. Those recently observed have been found to change into nebulae; a mass of glowing gas emitting the bright spectral rays of hydrogen and other gases. Photographs and spectroscopic observa tions give evidence of some explosive action, throwing out corpuscles with immense velocity in every direction, but throw no light on the origin of the explosion.
Star One of the remarkable fea tures of the heavens revealed by the telescope consists in star clusters — great numbers of these bodies crowded into a space which, meas ured by the expanse of the heavens, must be comparatively limited. It is not at all uncom mon to find hundreds of stars in a single bunch so closely packed together that, to the naked eye or in a small telescope, nothing is seen but a minute patch of light. One of the most re markable of these contains 60,000 stars, situated in the constellation Hercules, another in the constellation Centaurus was described by Sir John Herschel as one of the most remarkable objects in the heavens. There exists every variety of such clusters, from these closely packed ones to the agglomerations of the Milky Way, which any careful observer of the heavens can see on any clear evening during the late summer and autumn. Close together as the component stars of these clusters appear to be there is no doubt that they are really sepa rate from each other by distances vaster than those which separate the planets of our solar system; otherwise the most powerful telescope would not distinguish them as separate stars, but present them to our view as if confused to gether in one mass of light.
By several different methods the distances from us of the globular clusters have very recently been found by Shapley of the Mount Wilson Solar Observatory. It is shown that while the cluster in Centaurus is the nearest, the more distant are not infinitely remote from our Milky Way cluster, but are outside of it and apparently connected with it. They are, in short, now known to be small universes of stars, the distances through them being meas ured in hundreds of light years instead of in tens of thousands as in the case in our Milky Way cluster.
It is a remarkable fact that many of these clusters contain a great number of variable stars. This fact, taken in connection with the probable cause of variability already men tioned, makes plausible the idea that close binary systems are very numerous in the clusters. If, at any one moment, all the stars of the cluster were at rest, they would in course of time be drawn together by mutual gravitation. Each star must, therefore, be in motion relative to the others, describing some kind of an orbit around their centre of gravity.
The laws of revolution in cases like this must be very complicated, but as they require thousands of years to go through their changes and accurate observations have been made for hardly more than a century, astronomers are not yet able to investigate them fully.
Constitution of the is no reasonable doubt that the general constitution of the stars is the same as that of our sun; and that they consist of masses of intensely hot vapors of the substance composing them, com pressed together by the mutual gravitation of their parts. As we have already said, the stars are composed in the main of the substances found to exist in the sun, but, probably, in a great variety of forms as regards density and temperature. The spectra of the stars, consist ing, as most of them do, of a bright continuous spectrum crossed by dark lines, show that we see the luminous surface through an atmos phere cooler than itself, though really intensely hot.