348 ANNUAL REPORT SMITHSONIAN INSTITUTION, 19 64 



In 1957 the most popular hypothesis on the heating of the upper 

 atmosphere was Chapman's idea that the heating occurred by con- 

 duction from a hot interplanetary space that was part of the solar 

 corona. The belief was that the earth moved in a thin medium with 

 a temperature of something of the order of a quarter of a million to 

 possibly a half -million degrees and that this heat percolated by con- 

 duction into the atmosi)here. This conception proved to be completely 

 wrong, for in fact the temperature of the upper atmosphere above a 

 given point of the earth and at a given time is just about constant from 

 300 km. upward, at a relatively cool level, about 1000° to 2000° Kelvin. 



Both the extreme ultraviolet radiation and the heating energy from 

 the corpuscular flux from the sun seem to be absorbed at comparable 

 heights of the order of between 100 and 200 km. above the earth. 

 This layer has the same role for the upper atmosphere as the ground 

 has for the troposphere, except that instead of convection there is only 

 conduction. The lower regions heat the upper regions. The extreme 

 ultraviolet and the heating energy from the corpuscular radiation 

 directly heat the atmosphere, and then heat the layers above by 

 conduction. 



The temperature of the atmosphere does not increase constantly 

 as one goes upward. Actually, it increases in a tremendous leap 

 in the region between 100 and 200 km., going from 200° Kelvin at 

 90 km. to a possible 2000° Kelvin at maximum sun activity in a matter 

 of 100 to 200 km. Then it remains stationary in the higher regions 

 of the atmosphere. In other words, it is almost an inverted picture 

 from what had been anticipated before the IGY. 



In summary, extreme ultraviolet radiation from the sun heats the 

 atmosphere unequally in the dark and bright hemispheres and thus 

 causes the diurnal effect, and it varies from day to day and therefore 

 creates the erratic "27-day''' effect, as well as the 11 -year variations. 

 Corpuscular radiation from the sun indirectl}^ heats the atmosphere 

 during magnetic storms and may or may not be related to the mys- 

 terious semiannual effect. These, then, were some of the major scien- 

 tific results derived from optical observations of satellites during the 

 IGY. 



Scientists at the Observatory also undertook other research pro- 

 grams as part of the IGY. From observations of Satellites 1957 

 /?1 and 1957 ^82, Dr. Jacchia derived new values for the second- 

 and fourth-order coefficients of the earth's gravitational potential. 

 Dr. Kozai made a theoretical study of the motion of a satellite by 

 taking into account tlie second-, third- and fourth-order terms of the 

 earth's potential; his results provided more accurate expressions for 

 the secular motions of the perigee and the node. He also developed 

 a theory of secular peilurbations on satellite motions caused by the 

 sun and the moon. Other scientists began developing further means 



