SUN 



5625 



SUN 



tates on its own axis in twenty-six days, and 

 completes a circuit of the heavens in a year. 



Composition and Heat of the Sun. What is 

 behind the photosphere and the chromosphere, 

 what the sun consists of in its interior, is still 

 more or less a matter of conjecture. The sun 

 apparently burns, but not in the same way that 

 a piece of wood burns and is consumed. If the 

 sun is cooling, the process is so gradual as never 

 to have been in the slightest degree noted. 

 Since the earth has been inhabited there has 

 been time for the sun to burn itself out, but it 

 is agreed that it still contains enough heat to 

 supply the earth for at least 10,000,000 years. 

 In the gaseous mass composing the sun are 

 present iron, titanium, calcium, manganese, 

 nickel, cobalt, chromium, barium, sodium, mag- 



000 miles. These are called sun spots, and it is 

 observed that they become more numerous at 

 regularly recurring intervals. Although appar- 

 ently dark, sun spots are only dark in compari- 

 son with the rest of the sun's surface. In 

 reality, the light of even the darkest of sun 

 spots far exceeds limelight in brilliance. The 

 brightest part of an electric arc light is the near- 

 est approach to the light of the sun, but even 

 that is not one-quarter as bright as the solar 

 surface. It is of course quite impossible to ex- 

 amine sun spots with the naked eye. Colored 

 or smoked glass screens should be used to pre- 

 vent the glare from damaging the eyes. The 

 Carothers Observatory, Houston, Texas, sug- 

 gested a practical method for observation of 

 sun spots as follows : 



SUN SPOTS, REPRODUCED FROM PHOTOGRAPHS 



At left, spots seen near edge of the sun. The second illustration shows a spot, rounded at first, 

 finally becoming bridged over with projections, as seen in the third picture. 



nesium, copper, hydrogen, zinc, sulphur, cerium, 

 strontium and potassium; each of these is de- 

 scribed in its place in these volumes. The 

 amount of heat received by the earth from the 

 sun in a year would melt a covering of ice 124 

 feet thick all over the surface of the earth, and 

 if the rays from the sun could be all concen- 

 trated on to a bridge of ice 2% miles thick 

 reaching from the earth to the sun, the heat 

 would be sufficient to melt that bridge in one 

 second. Only a very small portion of the heat 

 radiated by the sun reaches the surface of the 

 earth, and the portion which does reach the 

 surface does not come direct, or it would scorch 

 and destroy all plant and animal life. The 

 earth is still further protected by its inclina- 

 tion on its axis, or the angle at which it jour- 

 neys round the sun, causing the sun's rays to 

 fall obliquely on its surface. If the same face 

 of the earth were always turned toward the sun, 

 one-half would be always in the light and heat, 

 the other half in perpetual darkness and cold. 



Sun Spots. The surface of the sun appears 

 to be dotted with dark patches, irregular in 

 shape and varying in diameter from 100 to 100,- 



"If images of the sun be formed through clean- 

 cut, round holes of proper size in a darkened 

 room, at sufficient distance from the aperture and 

 cast upon white paper or cardboard, sun spots 

 of ordinary size may be readily seen on the 

 image." 



This would enable amateurs to note the 

 progress of the spots across the solar disk and 

 to compile interesting records. By observation 

 of sun spots which pass round the sun, the time 

 of the sun's rotation is calculated. The spots 

 are apparently not attached to the sun's sur- 

 face but float about somewhat as clouds do in 

 our atmosphere, causing differences in the cal- 

 culated time of rotation according to the points 

 from which spots are observed. The theory 

 that sun spots are cavities filled with cooler 

 gases than those in the surrounding region has 

 been practically proved incorrect. It might be 

 concluded that sun spots are really eruptions 

 breaking through the photosphere. 



Influence of Sun Spots. It has been clearly 

 established that when sun spots are most 

 numerous magnetic storms are frequent and 

 violent on earth; it is also believed that the 

 brilliance of the aurora borealis is directly con- 



