SUN 



5624 



SUN 



UN, the most conspicuous of the heav- 

 enly bodies and the center of the solar system, 

 regarded by astronomers as a star, and believed 

 to be a gaseous mass, perhaps similar to the 

 nebula from which the universe may have been 

 evolved. The earth is dependent on the sun 

 for heat and light; no form of life could exist 

 on the planet we inhabit if the influence of 

 the sun were withdrawn. To us on earth the 

 sun is therefore by far the most important 

 object in the solar system; in reality, though, 

 it is only one of thousands of stars, and not 

 even one of the largest. The stars are centers 

 of their own systems. 



The Sun's Surface. All that can be seen of 

 the sun by an observer on the earth is merely 

 its shining surface, so intensely bright that the 

 naked eye cannot endure to look at it. As- 

 tronomers call this shining surface the photo- 

 sphere. A cloak, or envelope, of burning hy- 

 drogen, surrounding . the sun, is called the 

 chromosphere, which shows red, like a burning 

 mass, through the spectroscope. The promi- 

 nences observable are vast planes of hydrogen 

 extending up through the chromosphere, thou- 

 sands of miles high, beside which the earth 

 would be but a speck. During eclipses there 

 may be seen a still more vast, luminous enve- 

 lope, called the corona. 



Size and Density. The diameter of the sun 

 is 866,500 miles, or 109y 2 times that of the 

 earth; its distance from the earth, about 93,- 

 000,000 miles. It would take fourteen years for 

 sound to travel from the sun to the earth. If 

 an explosion occurred on the sun and the sound 

 could possibly travel so far we should hear the 

 explosion fourteen years after it had happened. 

 The sun's volume is 12,000 times and its sur- 

 face area 1,300,000 times that of the earth. Its 

 density is 1.41 times that of water, so it is 

 much less dense than the earth, whose density 

 is 5% times that of water. 



Gravity on the sun's surface is 27.6 times as, 

 great as on earth; a person weighing 150 

 pounds on earth would weigh nearly two tons 

 on the sun, and a body falling on to the sun's 

 surface would fall 444 feet the first second, 

 while on the earth the fall the first second 

 would be 16.08 feet. On the sun's surface, 

 if it were possible to get there, a human being 

 could not lift hand or foot, but would probably 

 be crushed by his own weight. 



Apparent Motion. To dwellers on earth the 

 sun appears to move through the heavens. As 

 a matter of fact, the earth moves round the 

 sun, but we are unable to feel that motion. 

 In the spring the sun rises a little farther north 



Mercury ^ Venus 



Uranus 



Jupiter Saturn 



Neptune 



Earth Mars 



COMPARATIVE SIZES 

 The sun is represented by the large outer circle. 



of east each day for three months in the north- 

 ern hemisphere. At the summer solstice, it 

 appears to stay at the same height for a few 

 days, then starts on its journey southward. It 

 not only moves north and south, but continu- 

 ally advances eastward among the stars, ro- 



