502 



TABLE 512.— MAGNETIC AND ELECTRIC DATA FOR SUN AND EARTH 



(Chapman, Cosmical magnetic phenomena, Nature, vol. 124, p. 19, 1929.) 



Sun's magnetic field too small to be measured by direct effects on earth; measured by 

 Zeeman effect on spectrum lines. 



Earth's magnetic axis inclined 12° to rotation axis. 



Earth's field rotates at same speed as nearly rigid earth. 



Earth : Polar intensity of field $ gauss. 



Sun : Intense local fields frequent, 3000 gauss. The magnetic field of spots reverses each 

 cycle (Proc. Astron. Soc. Pacific, vol. 41, p. 136, 1929). The polarity of leading spot in a 

 bipolar group in the Northern Hemisphere is opposite that in the Southern Hemisphere- 

 relationship reverses each new sunspot cycle •'• complete magnetic cycle is double sun- 

 spot cycle. 



Specific resistances : Earth Sun (Chapman, loc. cit.) 



Heaviside layer, 10 10 Reversing layer, 3 X 10 10 



Dry earth, 10" to 10 16 Photosphere, 10", T, 10000°K. 



Sea water, 2 X 10 10 Center, 3 X 10 s , T, 4 X 10 7 



200-600 m deep, 3 X 10" 



Further characteristics of spots: (Milne, Monthly Notices, Roy. Astron. Soc, vol. 90, 

 p. 487, 1930.) Umbra (dark center), 800 (very small) to 80,000 km across: penumbra 

 may reach 240,000 km. Generally short-lived. A few last several (3) rotations, very 

 rarely 6; one in 1840, 18 months. Most occur in 2 belts 5° to 40° N. and S. latitudes, 

 often occur in pairs (see above). Umbra temperature 4000° K. Evershed gives velocity of 

 outburst from spot 2 km/sec. 



SMITHSONIAN PHYSICAL TABLES 



