360 THE SUN'S GIFT OF LIGHT 



Sometimes the sun or moon is surrounded by bright 

 rings called, when of small diameter, coronas, and when of 

 great diameter, halos. These rings are due to the effect 

 of water or ice particles on the light coming from the sun 

 or the moon. 



Under certain conditions it may happen that light com- 

 ing from objects at a distance is so refracted and reflected by 

 the layers of air of different density, through which it comes 



LICK OBSERVATORY 



As light is affected by the atmosphere, observatories must be placed 

 where atmospheric conditions are the best. This famous observatory 

 is on a mountain in the clear air of California. 



to the eye of the observer, that objects appear to be where 

 they are not, like the image of a person seen in a mirror. 

 This phenomenon is called mirage or looming. It occurs 

 most frequently on deserts and over the sea near the coast. 



Sometimes in high latitudes arches and streamers of 

 colored light are seen illuminating the northern sky. The 

 brilliancy and colors of the illumination vary. Sometimes 

 it is bright enough to be seen even in the daytime. This 

 display is called the aurora borealis or " northern lights " 



