Astronomical Photography from the 

 Stratosphere ' 



By Martin Schwarzchild 



Eugene Higgins Professor of Astronomy, Princeton University 



[With 2 plates] 



Throughout the centuries astronomers have labored under one 

 enormous handicap that has set harsh limits to all their observational 

 work. Between celestial objects which are the subject of the astrono- 

 mer's research and his telescope lies the earth's atmosphere, a murky 

 restless layer which forever garbles our only source of information 

 on the universe around our earth. This handicap imposed by the 

 earth's atmosphere has made itself felt most strongly in three broad 

 areas : First, no ultraviolet light with wavelengths shorter than 3,000 

 angstroms can penetrate the earth's atmosphere at all; this loss of 

 the ultraviolet prohibits us from studying the bulk of the light 

 emitted from the hottest and most energetic stars and prevents us 

 from making accurate measurements regarding many of the astro- 

 nomically most important chemical elements which have their main 

 absorption lines in this spectral region. Second, large blocks of the 

 infrared spectnim are completely blocked out by the earth's atmos- 

 phere and thus we have been unable to study the cooler stars in detail 

 and to measure the absorption bands of many of the key chemical com- 

 pounds. Third, even the ordinary visible light, though not absorbed 

 by the earth's atmospliere — or at least absorbed only to a minor 

 degree — does not reach our telescopes ungarbled; the turbulence of 

 the atmosphere bends the light rays from the stars slightly and thus 

 prevents us from getting as sharp pictures of the celestial bodies as 

 our instruments otherwise would permit. Even at the best mountain 

 observatories on those rare occasions when the atmosphere above be- 

 Iiaved relatively quiescently only a veiy small number of astronomical 

 photographs have been obtained which show details as small as half 

 a second of arc; this angle corresponds to half a mile on the moon, 



1 The 28th annual James Arthur lecture on the sun, given under the auspices of the 

 Smithsonian Institution on May 8, 1962. 



323 



