THE UNIVERSE IN WHICH WE LIVE n 



sphere, since such a place is in the illuminated part of the earth 

 for a longer time than it is in the dark part. Moreover, the sun's 

 rays strike the earth more nearly vertically in this latitude than 

 they do in position c, and so they are more powerful. In position a 

 there is summer in the Northern Hemisphere, for the long days 

 give the sun time to impart more heat than is lost in the rela- 

 tively short nights, and the nearly vertical rays are very effective, 

 losing relatively little of their heat as they pass through the air. 



In position c, however, the Northern Hemisphere is having 

 winter, for the days are short and the nights are long, while the 

 sun's rays strike the earth obliquely and so glance off readily; 

 they lose much of their heating effect also, since they must pass 

 through a long stretch of atmosphere that reflects much of their 

 heat. 



In positions b and d the circle between the dark and the 

 illuminated sides passes through the North and South poles, 

 and so the days and nights are of equal length all over the earth. 

 These points of the earth's orbit are therefore known as the 

 equinoxes. Points a and c are called respectively the summer 

 and winter solstice, for the sun appears to cease its northward or 

 southward journeying and to stand still for a few days before it 

 begins to move back toward the celestial Equator. 



Just as the planets travel in pathways about the sun, so there 

 are bodies that we call moons, that travel in orbits about the 

 planets. Our earth has one such, the queen of the night; Mer- 

 cury and Venus, so far as we know, have none; Mars has two 

 very small ones, probably not over 10 miles in diameter; Jupiter 

 has seven, four large ones and three small; Saturn has ten, one 

 of which is larger than the planet Mercury; Uranus has four and 

 Neptune, one. 



Our moon has been from time immemorial a god or goddess 

 worshiped by primitive man. The Assyrians adored her as 

 Ashtaroth; the Egyptians, as Isis; the Greeks named the moon- 

 goddess Selene, or Phoebe and, later, Artemis, while the Romans 

 called her Diana or Luna. The ancient Aztecs adored her as 



