Is Space All Aglow? 



The new startling theory advanced by Professor Barnard to 

 explain non-luminous bodies brought out in relief against the sky 



The photograph on the 

 left is a luminous neb- 

 ula which is a mass of 

 gas. But w h a t is the 

 curious irregular hole 

 among the stars in the 

 photograph on the 

 right? These black 

 holes are supposed to 

 be openings in the rich 

 regions of the stars. 

 Professor Barnard is 

 inclined to the belief 

 that the supposed holes 

 are feebly luminous 

 bodies, and that they 

 were once bright like 

 the nebula shown at 

 the left, but have' lost 

 their light and become 

 blackened with age 



THERE is coming to the front the con- 

 sideration of the dark spots in the 

 sky. Professor Barnard of the Yerkes 

 Observatory has been studying this side 

 of the question lately, and the results that 

 he has already obtained lead him to 

 speculations that are both new and interest- 

 ing. 



The nebulae of the sky have generally 

 been considered to be intensely hot. These 

 huge masses of luminous gas would cool 

 aixi contract until, after millions of years, 

 the more compact stars were formed. The 

 stars might cool further until no light 

 could be seen coming from them; but it 

 was not generally believed that the gases 

 of the nebulae themselves could cool and 

 still remain in the gaseous state. One of 

 the first results of Professor Barnard's 

 work, however, was to lead him to believe 

 differently. Let us follow him through his 

 reasoning. 



He says that in photographing the sky, 

 large dark markings have often been 

 noticed in the photographs. At first blush 

 they seem merely huge openings in the rich 

 region of stars through which one looks 

 out into the blackness of the space beyond. 

 Although there are undoubtedly such va- 

 cancies, the more one becomes familiar 

 with others of them, the less this explana- 

 tion appeals. 



To suggest the true explanation, Profes- 

 sor Barnard has prepared the pair of photo- 

 graphs appearing on this page. These, he 



explains, have been made exactly to the 

 same scale, and a striking resemblance is 

 seen between the two objects that stand 

 out in them. But one is an ordinary 

 luminous nebula, and the other is a dark — 

 what? His observations induce him to 

 believe that it, too, is a nebula, but one in 

 which the great mass of gas has finally 

 cooled and lost its light. The gas of the 

 nebula, like many others that Professor 

 Barnard has studied, is still dense enough 

 to take definite outline and to stand out 

 against the luminous background behind. 

 But right at this point we would be led 

 to still another conclusion. There are 

 dark spots having very definite outlines to 

 be seen in the heavens, where, there is 

 every evidence to believe, there are neither 

 luminous stars nor luminous nebulae to 

 light up a background for them. What 

 then, is the cause for the luminous back- 

 ground in such cases? There seems to be 

 but one possible explanation, and that is 

 that space itself is luminous. Space itself 

 might be filled with the feeblest luminosity, 

 so feeble, indeed, that at the tremendous 

 distances to the fixed stars it is not even 

 perceptible to sight. Then, as space is sup- 

 posed to be of infinite extent, this luminosity 

 will increase in apparent density until, 

 finally, it would become dense enough to 

 affect a sensitive photographic plate. Only 

 in this way would it be possible to explain 

 how non-luminous objects could be brought 

 out in relief in these parts of the sky. 



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