] Recognizing the Stars 



What Comets are Made of: A comet has a bright starlike head and 

 a long filmy tail. We know that it is made partly of solid matter 

 (as it reflects sunlight) and partly of gas; but the solid matter 

 does not form one great solid body like the earth. It is made of 

 many solid pieces of greatly varying sizes with gases between them. 



Millions of Miles, Thousands of Years: The tremendous distance 

 that separates us from the comets makes them appear small. Ac- 

 tually the head of a comet may be as big as the earth, if not much 

 larger, and the tail is millions of miles long! The apparent motion 

 of comets through space is affected, too, by this distance. They 

 seem to move slowly because they are millions of miles away, but 

 they are really speeding through space. In the course of their 

 travels which take them around the sun in elongated ellipses 

 they may return a number of times within sight from the earth, 

 but hundreds or thousands of years may pass between the suc- 

 cessive appearances of any one comet. 



While the actions of most comets are unpredictable, the famous 

 "Halley's comet" a bright one that can easily be seen without a 

 telescope has been observed at intervals of about seventy-seven 

 years. It was last seen in 1910 and is predicted to return about 

 1987. 



A comet may be seen with the naked eye or with a telescope for 

 a number of nights, perhaps running into weeks. Each night its 

 position is somewhat changed as it progresses through the heavens. 



"SHOOTING STARS" ARE NOT STARS 



The term "shooting star" is a very natural one for a bright 

 spot streaking across the sky. Astronomers avoid the term, how- 

 ever, as the objects that look like shooting stars are not stars at 

 all. The proper name for them is meteors. 



Meteors and "Fireballs": Meteors are made up of solid material 

 that suggests stone or iron. We do not know whether meteors are 

 fragments left over from the forming of our planets or matter 

 that entered our solar system from the outside; but we do know 

 that comets sometimes break up into meteors. 



