TABLES 808-824.— SOLAR RADIATION * 



719 



TABLE 808.— THE SOLAR CONSTANT 



A long series of measurements has been made" 9 at widely separated, selected stations 

 by the astrophysicists of the Smithsonian Institution on both the total intensity of the 

 solar radiation and the spectral distribution of this radiation. One result of these measure- 

 ments is the value of the solar constant, that is, the total solar radiation (cal cm" 2 min" 1 ) 

 at normal incidence outside the atmosphere at the mean solar distance. As a result of the 

 work up to 1913 the solar constant was found to be 1.9408 ly. min" 1 (langley ; see Table 2, 

 Part 2). Later investigations 250 showed that the standard used in these measurements was 

 somewhat in error. Observations showed that the correction employed for the unmeasured 

 ultraviolet radiation was too low ; also solar radiation in the infrared region beyond about 

 2.5 fi introduced some error. As a final result of all the corrections it was found that this 

 1913 value of the solar constant was very good. It should be pointed out that there is 

 evidence 24B that the solar constant fluctuates as much as± 1.5 percent. In addition, the 

 varying distance between the sun and earth (see Table 827) produces a change in the actual 

 solar radiation at the top of the atmosphere of about ± 3.5 percent from the mean value. 

 Now in 1951 the value of the solar constant (amount of energy falling at normal incidence 

 on one square centimeter per minute on body at earth's mean distance) = 1.946 calories = 

 mean 6430 determinations 1924-47. Subject to variations, usually within the range of 2.8 

 percent, and occurring irregularly in periods of a week or 10 days. New data on the ultra- 

 violet and infrared corrections to the solar constant given by F. S. Johnson (in press) 

 indicate that the value 1.946 should be increased by 2.6 percent. Johnson's best value is 

 2.00 ± 2 percent. 



Computed effective temperature of the sun : from form of blackbody curves, 6000° to 

 7000° Absolute; from \ m a* 7 = 2930 and max = 0.470m, 6230°; from total radiation, J = 

 76.8 X 10" 12 X T\ 5830? 



Sun radiates 3.8 X 10 38 erg/sec 



6.25 X 10 10 erg sec" 1 cm" 2 

 of this 1.72 X 10 2 ' erg/sec strikes the earth. 



* Prepared by L. B. Aldrieh and W. H. Hoover, Astrophysical Observatory, Smithsonian Institution. 



249 Abbot. C. G., Solar radiation and weather studies, Smithsonian Misc. Coll., vol. 94, No. 10, 1935. 



260 Aldrieh, L. B., and Abbot, C. G., Smithsonian pyrheliometry and the standard scale of solar radia- 

 tion, Smithsonian Misc. Coll., vol. 110, No. 5, 1948. See also Annals, Smithsonian Astrophysical 

 Observatory, vol. 7, ch. 3 (in press). 



TABLE 809.— ATMOSPHERIC TRANSMISSION COEFFICIENTS 



High transmissions are for every clear day and low precipitable water, 2 mm for Monte- 

 zuma and Table Mt., and 3.5 mm for Miam'. 



Low transmissions are for very hazy days and high precipitable water, 10 mm for Monte- 

 zuma and Table Mt., and 25 mm for Miami. 



Transmission coefficients in the range .70 — 2.25 X are all smooth-curve values drawn over 

 the tops of the water-vapor bands. 



Unit air mass. 



SMITHSONIAN PHYSICAL TABLES 



