THE HEAVENS IN NOVEMBER 



189 



faintness next May, when it will shine 

 as a star of the 13.2 magnitude, only 

 visible in the largest telescopes. Thus 

 the changes in this distant sun are 

 even more remarkable than those of 

 the celebrated Mira, at R, Figure 1. 

 We know that its wonderful blazes of 

 light are partly caused by outpourings 

 of luminous hydrogen, and its spectrum 

 clearly indicates the agitation and 



brated Demon Star, Algol, whose light 

 is periodically cut off by the passage 

 of its dimmer companion between itself 

 and us. This star will reach its great- 

 est faintness on November 2, at 7 

 hours 22 minutes P. M. ; on Novem- 

 ber 20, at o hours 16 minutes A. M. ; on 

 November 22, at 9 hours 5 minutes P. 

 M., and on November 25, at 5 hours 

 'A minutes P. M. The observer must 



NDgTH 



SOUTH 



Figure 1. The Constellations at 9 P. M., November 1. (If facing south hold the map upright. If facing 

 east hold "East" below; if facirg west hold "West" below. If facing north hold the map inverted.) 



violent motions of its heated materials 

 at these times, but of the real cause 

 of the periodic disturbances we are still 

 ignorant. 



Not only should the observer watch 

 this star from time to time during the 

 coming weeks, to observe its gradual 

 fading away, but he may also be inter- 

 ested in examining the well-known 

 Mira, at R, Figure i, and the eclipsing 

 variable at T. The former of these, 

 which last May was nearly as bright 

 as the North Star, is now barely visible 

 to the eye, though it will not reach its 

 greatest faintness of 9.6 magnitude until 

 next December. The latter is the eele- 



not expect to see the light of the star 

 suddenly cut off; the companion moves 

 before the brighter star so gradually 

 that four and one-half hours elapse be- 

 tween time of greatest faintness. By 

 looking at the star at intervals of per- 

 haps an hour its light changes are, 

 however, easily observed. 



STARS LESS DENSK THAN AIR. 



From a study of the stars of this kind 

 we can not only ascertain the nature 

 of these double sun systems but we can 

 also find approximate!}' how dense the 

 two bodies are. And it is found that 

 many of them are remarkably rare and 

 tenuous — merely nebulous masses 



