On the track of discovery :    riddles of outer space, etc. 

 - Moscow :    Progress Publishers ,    1967 
 - 237 p. :    ill. ;    21 cm. 
<br/><br/><label>Subjects--Topical Terms: </label><br/> Astronomy.
<br/><br/><label>Dewey Class. No.: </label>520 ONT