384 I Our Earth and Its Fellow Planets 



Telescopes for Everyday Use 



If your family becomes seriously interested in stargazing, you 

 may consider a telescope of your own a worth-while investment. 

 Either of the two types that are used by the great observatories 

 devoted to astronomy, can be obtained in vastly reduced size. 



REFRACTOR TELESCOPES 



The kind that looks as you might expect it to that is, 

 resembling a long spyglass is known as a refractor, or lens, tele- 

 scope. It is called a ''refractor" because starlight, as it passes 

 through the lens, is bent or refracted by the curved surface of the 

 glass, then brought together at the focus. 



REFLECTOR TELESCOPES 



The other type is a "reflector" or mirror telescope. It brings 

 the light from the stars to a focus by reflection from a mirror, 

 which is not flat like an ordinary mirror but slopes gradually 

 towards its center. The world-famous telescope on Mt. Palomar 

 in California is a reflector. 



Each type, refractor and reflector, has its advantages for the 

 professional astronomer, but on the whole the refractor seems 

 best for a child. It is less subject to damage from inexperienced 

 handling and as a rule the stars are seen more sharply through it. 



Choosing a Telescope: If you are buying a telescope, it is wise to 

 choose a small one with a good lens and a tripod (mounting) , 

 rather than a large one without these assets. A mounting that is 

 not firm will show you "dancing stars" as you look through it. 

 Equipment of this kind may require an investment of more than a 

 hundred dollars; however, you may find satisfactory an extension 

 type of telescope that is held to the eye. The cost of such an instru- 

 ment is less than half that of a mounted telescope. 



In many towns and cities groups of young people interested in 

 the stars have astronomy clubs. Belonging to such an organization 

 often gives a child the opportunity to use a telescope regularly, 

 thus saving his family the expense of investing in one. The club 



