SOLAR VARIATION AND WEATHER? 
By CuHartes G. ABBOT 
Former Secretary, Smithsonian Institution 
[With 2 plates] 
NATURE OF THE SUN 
The sun is a gaseous body 860,000 miles in diameter of about 330,000 
times the mass of the earth. Though so hot that neither solids nor 
liquids exist in it, the force of gravity due to its enormous mass com- 
presses the sun’s gaseous substance to an average density nearly 1.5 
times that of water, or nearly 1,100 times that of air at sea level. This 
density prevails, notwithstanding that the great temperature not only 
gasifies the chemical elements, but still further subdivides them by ion- 
izing them strongly. They are no longer composed of molecules, like 
gaseous substances that we find in the laboratory, or even complete 
atoms, for the atomic nuclei have lost some of the ions which at lower 
temperatures would surround them to make up complete atoms. The 
surface temperature of the sun is of the order 6,000° Centigrade, or 
10,800° Fahrenheit, nearly twice as hot as the are light. Within the 
sun the temperature rapidly rises, and at the sun’s center it is supposed 
to be many millions of degrees. At such enormous temperatures and 
with its immense surface, the sun is a tremendously powerful radiator, 
so powerful that at the earth’s mean distance, 93,000,000 miles, the 
sun’s average radiation in free space measures 1.94 calories per cm.? per 
minute. This value is called the solar constant of radiation. It im- 
plies that the earth, which is about 8,000 miles in diameter, receives 
all the time from the sun the heat equivalent to a quarter of a quadril- 
lion horsepower (1075/4 hp.) 
SOLAR ROTATION 
The sun, like the earth, rotates on an axis. The sun’s axis is not 
exactly parallel to the earth’s, but inclines toward a point halfway be- 
between the Pole Star and Vega at 26° from the North Pole. It has 
1The twelfth Arthur lecture given under the auspices of the Smithsonian Institution, 
February 29, 1944. 
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