713 



TABLE 800.— RADIATION AT EARTH'S SURFACE, MASS AND RADIATION 

 DENSITY IN OUR GALAXY, AND IN THE UNIVERSE 



Our galaxy: 



Total number of stars 30X 10" 



Average mass of stars 2X 10™ g 



Total mass of galaxy 3.27X 10" g 



Total volume 10 98 cm 3 



Diameter (disk) 5x10" cm 



Average mass density 3X 10" g cm" 3 



Total mass energy 2.95X 10* ergs 



Total kinetic energy 1.6 X 10 90 ergs 



Average mass-energy-density 3x10"' erg cm" 3 



Average kinetic energy-density 1.6X 10~ 8 erg cm" s 



Universe: 



Mass density 3X 10 s0 g cm" 3 



Mass-energy-density 3X 10"* erg cm" 3 



Radiant-energy-density 6X 10" 19 erg cm" 3 



Cosmic ray energy-density 1.7X10" 11 erg cm" 3 



At earth's surface (top of atmosphere) : 



Total radiant energy from all stars 1.78X 10" 3 erg cm" 2 sec" 



Total radiant energy density (our galaxy) S.8X10" 14 erg cm" 3 



Total radiant energy (sun directly overhead)* 1.2X10 9 erg cm" 2 sec" 



Cosmic ray energy 3.8X 10" 3 erg cm" 2 sec" 



Cosmic ray energy-density 10" 13 erg cm"" 



* Astrophysical data. 



TABLE 801.— COMPOSITION OF COSMIC RADIATION AT GEOMAGNETIC 



LATITUDE 30° *» 



Relative No. of particles Relative No. of particles 



t A 



Nuclei Sun t Sco Cosmic rays 



H .... 1.6X10 6 1.6X10 9 



He .... 2.9X10 S 4.0X10 5 



6^Z^8 3200 2500 14000 



2 « Bradt and Peters, Phys. Rev., vol. 77, p. S4, 1950. 



SMITHSONIAN PHYSICAL TABLES 



