Sky Study 913 



THE RELATIONS OF THE SUN TO THE EARTH 



Teacher's Story 



"Whether we look or whether we listen, 

 We hear life murmur or see it glisten." 



LOWELL. 



All this murmuring and glistening life on our earth planet has its source 

 in the great sun which swings through our skies daily, sending to us through 

 the friendly ether his messages of light and warmth messages that kindle 

 life in the seed and perfect the existence of every living organism, whether it 

 be the weed in the field or the king 011 his throne. 



At sunrise this heat which the sun sends out equally at all times of day 

 and night, is tempered when it reaches us because it passes obliquely through 

 our atmosphere-blanket, and thus traverses a greater distance in the cooling 

 air. The same is true at sunset ; but at noon, when the sun is most directly 

 over our heads its rays pass through the least possible distance of the at- 

 mosphere-blanket and, therefore, lose less heat on the way. It is true that 

 often about three o'clock in the afternoon is the hottest period of the day, 

 but this is because the air-blanket has become thoroughly heated ; but we 

 receive the most heat directly from the sun at noon. 



The variations in the time of the rising and the setting of the sun may be 

 made a most interesting investigation on the part of the pupils. They 

 should keep a record for a month in the winter ; and with this as a basis, use 

 the almanac to complete the lesson. Thus, each one may learn for himself 

 which is the shortest and which the longest day of the year. There is a 

 slight variation in different years; the shortest day of the year when this 

 lesson was written, as computed from a current almanac, was the 22d of 

 December; it was nine hours and fourteen minutes long. The longest day 

 of the year was the 22d of June, and it was fifteen hours and six minutes in 

 duration. On the longest day of the year the sun reaches its farthest point 

 north and is, therefore, most nearly above us at mid-day. On the shortest 

 day of the year, the sun reaches its farthest point south and is, therefore, 

 farther from the point directly above us at mid-day than during any other 

 day of the year. 



Also the movement of the sun north and south is an interesting subject 

 for personal investigation, as suggested in the lesson. Through quite 

 involuntary observation, I have become so accustomed to the arc traversed 

 by the points of sunrise as seen from my home, that I can tell what month 

 of the year it is, by simply noting the place where the sun rises. When 

 it first peeps at us over a certain pine tree far to the south, it is Decem- 

 ber ; when it rises over the reservoir it is February or October ; and when it 

 rises over Beebe pond it is July. Only at the equinox of spring and fall does 

 it rise exactly in the east and set directly in the west. Equinox means equal 

 nights, that is, the length of the night is equal to that of the day. 



So vast is the weight of the sun that the force of gravity upon its surface 

 is so great that even if it were not for the white-hot fireworks there so con- 

 stantly active, we could not live upon it, for our own weight would crush us 

 to death. But this multiplying the weight of common objects by twenty- 

 seven and two-thirds to find how much they would weigh on the sun is an 

 interesting diversion for the pupils, and incidentally teaches them how to 

 weigh objects, and something about that mysterious force called gravity; 

 and it is also an excellent lesson in fractions. 



