The Evolution of the Universe 



11 



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Fig. 4. Edge-on diagram of our galaxy. The sun is indicated by the small 

 circle at the left, between the small numbers 0.5 and 1 in the left hand portion 

 of the disc. The scale is in kiloparsecs; one kiloparsec is 3,260 light years. 

 (After Oort.) 



Milky Way galaxy rotate at different rates, the central portion 

 making a complete revolution in 120 million years and the outer 

 portion including our solar system in 230 million years. What effect 

 this differential in speed will have on the future shape of the galaxy 

 is not known ( Oort, 1956 ) . 



