CHAPTERS ON THE STARS. 



21 



Another nebula which, though not conspicuous to the naked eye, 

 has attracted much attention from astronomers, is known, from the 

 figure of one of its branches as the Omega nebula. Sir John Herschel, 

 who first described this object in detail, says of it: "The figure is nearly 

 that of the Greek capital Omega, somewhat distorted and very un- 

 equally bright." From one base of the letter extends out to the east 

 a, long branch with a hook at the end, which, in most of the drawings, 

 is more conspicuous than the portion included in the Omega. The 



Fig. 11. The Great Spiral Nebula M. 33, Photographed with the 

 Crossley Reflector of the Lick Observatory. 



drawings, however, vary so much that the question has been raised 

 whether changes have not taken place in the object. As in other 

 cases, this question is one which it is not yet possible to decide. The 

 appearance of such objects varies so much with the aperture of the 

 telescope and the conditions of vision that it is not easy to decide 

 whether the apparent change may not be due to these causes. It is 

 curious that in a recent photograph the Omega element of it, if I may 



