The Evolution of the Universe 



Fig. 2. Galaxy NGC 4565 seen edge on. The dark streak through the length 

 of the galaxy is the disc of dust and gas. (Photograph from the Mount Wilson 

 and Palomar Observatories. ) 



The distances encountered in the universe are Kkewise as in- 

 comprehensible as the weights. The distance from the earth to the 

 moon is about 250,000 miles. Light, which travels at 186,000 miles 

 per second, covers this distance in I/2 seconds. The distance from 

 the earth to the sun is about 108 million miles, or 8 /^ light minutes, 

 and the distance from the earth to the nearby star Alpha Centauri 

 is a distance of 4.3 light years. The disc of our galaxy is some 80,000 

 light years across and 10,000 light years thick (Figs. 3 and 4). The 

 distance to the nearest neighboring galaxy, the Andromeda nebula, 

 is about 680,000 hght years. Our galaxy belongs to a cluster of 17, 

 the total group having a diameter of two million light years. Out- 



