THE SEASONS AND THE SOLAR SYSTEM 173 



winter the north pole is tipped (inclined) away from the 

 sun, while in our summer it is tipped toward the sun; in 

 the southern hemisphere, the reverse is true. Thus we 

 see not only why the sun gets higher at noon in summer 

 than in winter; we also see why the sun in summer remains 

 visible longer than in winter. Since in summer we are 

 tipped toward the sun, while in winter we are tipped away 

 from it, of course we see it longer in summer. Evidently, 



FIG. 62. Diagram to show the direc- FIG. 63. Diagram to show the direc- 

 tion of the sun's rays in summer; the tion of the sun's rays in winter; the 

 north pole is at the top. north pole is at the top. 



then, we haw found out why the days of summer are longer 

 than those of winter. We have found the cause of the sea- 

 sons. 



The Equinoxes. Midway between the shortest and 

 longest, days of the year come days when it is just twelve 

 hours from sunrise to sunset. These days are March 

 21 and September 22. On these days, and these days 

 only, the circle which bounds the sunlit half of the earth 

 passes through both poles. So all over the world, on these 

 dates, day and night are of equal length. These days are 

 called the equinoxes (aequus, equal; nox, night); the one 

 in March is called the vernal (per, spring) equinox; the 

 one in September, the autumnal equinox. Perhaps you 



