THK MOVEMENTS OF THE S'I'AKS. 



35 



but by this roundabout argument it is possible to plumb depths 

 inaccessible to the usual method. 



Also now that we know the distances we can calculate the 

 actual brightnesses of these bodies. It turns out that all of 

 them are more brilliant than the sun : — 



5 have a brightness from 5 to 10 times that of the sun. 

 18 „ „ „ 10 to 20 

 11 „ „ „ 20 to 50 



5 „ „ „ 50 to 100 



I do not want to give you the impression from this that our 

 sun is a very inferior star. The sun really occupies a very 

 respectably high position among the stars. But there is a very 

 natural tendency for us (in making these researches) to notice 

 the very bright exceptional stars and overlook the vast multi- 

 tudes of lesser bodies. I have little doubt that in this cluster 

 the thirty-nine stars that have been found are just the excep- 

 tionally bright lights, and there will be a whole host of fainter 

 ones to be picked out some day. 



It is possible to trace the past and future of this interesting 

 group ; 800,000 years ago it made its nearest approach to us, 

 being then about one-half its present distance. It is now 

 receding, and as it becomes more distant it will contract and 

 become more concentrated. At the same time the stars will 

 grow fainter. In 60 million years, if the motion is not dis- 

 turbed, it will look like a globular cluster about 20' in 

 diameter. 



It would be interesting to know if the well-known globular 

 •clusters seen with the telescope are really groups like this. It 

 is rather doubtful, but there is a great deal to be said for this 

 view. If that is so, w T e can form a fair idea of what globular 

 clusters are like, now that we have fairly full knowledge of one 

 specimen. The very nearness of this Taurus cluster makes it 

 lose effect as a picture ; the stars are brighter, but the concen- 

 tration is lost. A globular cluster is like an impressionist 

 picture : you must stand well away from it to see it to advan- 

 tage. 



We must now leave these special groups of intimately 

 related, though widely-scattered, stars, and turn to certain 

 vaguer but much more widespread laws of stellar movement. 

 If you take a region of the sky at random, and map out 

 the principal stars with arrows showing the way they are 

 moving, it is usually quite conspicuous that the arrows tend to 

 point in one special direction. Not all the stars are moving 



D 2 



