METEORS — WHIPPLE 



241 



the meteors in a shower strike our atmosphere in parallel paths so 

 that all their trails, when extended backward on the sky, tend to 

 meet in a point, or radiant (fig. 2) . The shower is then named for the 

 constellation in which the radiant appears. Some meteor streams are 

 uniformly dense so that when the earth crosses their orbit we can 

 always count on a good display — for example, the Perseid meteors 



APPARENT 

 RADIANT 



" 777?r ^ OBSERVER 



A ™OSP HERE 



Figure 2. — Trails and radiant of a meteor shower. Above the atmosphere the parallel 

 dashed lines show the real paths of the meteors Ai, A2, and A3; solid lines show their 

 apparent paths. In the atmosphere the arrows AB show the real meteor paths, and the 

 arrows AC show the paths as they appear to the observer. 



from August 9-14, and many bright Geminid meteors on Decem- 

 ber 12-13. Occasionally, as on October 9, 1946, meteors seem to 

 fall almost like rain, occurring as frequently as one a second. 



As we consider larger and larger bodies we find that with increasing 

 size they penetrate more deeply into the earth's atmosphere and appear 

 as brighter and brighter meteors. If a meteor is bright enough to 

 produce a flash of light that illuminates buildings at night or pro- 

 duces shadows, it is called a fireball. If it is accompanied by a de- 



