SOME PECULIARITIES OF THE NOV^. 



By E. E. BARNARD. 

 (Read April 21, ig22.) 



There are no more interesting objects in the sky than the nov«. 

 The suddenness with which they rise from a faint or obscure condi- 

 tion or even from absolute invisibihty, sometimes to outrank all the 

 other stars in the heavens, in some cases increasing their light as 

 much as a hundred thousand fold, is very wonderful. This great 

 rise in brightness requires only a few hours or a few days at most. 

 Their rapid physical changes, the various colors through which they 

 pass in their declining light, their later change to apparently a nebu 

 lous state, and their final return to what seems to be their original 

 condition which they attain in a few years' time, make them of the 

 greatest interest from every point of view. 



The novae remain at their greatest brightness for a very brief 

 period, which in some cases can be counted in hours. They then 

 begin to fade, at first rather rapidly, then slowly. With many halts 

 and minor outbursts they finally, in a few years' time, say from eight 

 to ten or fifteen years, return to their original brightness. This 

 interval of decline seems to vary in different novse. Though they 

 thus follow the same process of rapid change in brightness and physi- 

 cal condition, there are decided differences and peculiarities among 

 them that might suggest great dissimilarity in their pre-nova state. 



One fact that is peculiar to them, though not necessarily definite 

 in its character, is that with perhaps one exception (that of Nova 

 Coronse of 1866) all of the novse are found in the Milky Way. Of 

 course, there are vastly more stars in the Milky Way than outside of 

 it and therefore a greater chance for a nova to appear in it. There 

 are other evidences, however, that they really belong there. 



What was the original condition of a nova? Little is known of 

 the early history of these bodies — before their outburst of light. We 



PROC. AMER. PHIL. SOC , VOL. LXI., H, AUG. 3I, I922. 



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