THE LUMINOUS SURFACE AND ATMOSPHERE OF 



THE SUN^ 



By Bertil Lindblad 



Director, Stockholm" Ohservatory 

 Salts juhadcn, Sweden 



[With 3 plates] 



There is no process in nature more important to us than the radia- 

 tion of light and heat from the surface of the sun. The famous 

 American astronomer Charles E. St. John, of the Mount Wilson 

 Observatory, once expressed this in a lecture ^ in the following w- ords : 



Not only is the motion of tlie eartli in space controlled by the masterful sun, 

 but what is more directly evident, the sun is the source of practically all our 

 light and heat, without which life, as we know it, could not exist upon the 

 earth. Someone has said that if the earth were cut olf from all solar radiation 

 for a single month, all life would be extinguished and the world become a 

 frozen waste. It is not so evident, but as clearly true, that the energy stored in 

 wood, coal, oil, and gas has come to us from the sun. Under the influence of 

 sunlight, particularly of the red and blue components, the carbon dioxide of 

 the atmosphere is taken in by the leaves of trees and plants and acted upon to 

 form the complex constituents of plant growth, mainly compounds of carbon 

 with hydrogen, oxygen, and nitrogen. Their chemical transformation requires 

 the absoiiJtion of energy which is accumulated and stored in these compounds, 

 to be released and again transformed when they are burned rapidly in ordinary 

 combustion, or slowly in our own bodies. Every heart beat, every breath we 

 take, every thought, and every act performed draws its working power from the 

 accumulated solar energy stored up in plant and animal growtli. The trans- 

 formation of solar energy in plant growth takes place in the leaves under the 

 action of sunlight upon the green coloring matter, the chlorophyll. As heat 

 engines plants cannot be considered efiBcient, transforming as they do only 1 

 or 2 percent of the solar energy falling upon their leaves, but the energy supplied 

 is enormous; plants work continually during growth and store up energy in 

 permanent form ; these are favorable conditions and result in tremendous ad- 

 vantages for man. The energy of coal has waited for his touch many millions 

 of years and what, if any, escapes his wasteful use will endure uncounted 

 millions yet without loss of its potential energy. The energy of the sun is 

 stored in the water lifted into the atmosphere by the sun's power and carried 

 by wind-driven clouds to higher regions, whence it falls as rain or snow, ever 

 renewing the reservoirs and so rendering them a practically exlmustless source 

 of power. 



> Seventeenth James Arthur lecture, given under the auspices of the Smithsonian Institution on April 

 6, 1950. 



* The Adolfo Stahl Lectures in Astronomy, San Francisco, 1919. 



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