244 



THE GUIDE TO NATURE 



Evening Sky Map for October. 



BY PROF. AI.l-KlvD MITCIIIXL, OF COLUMBIA 

 UNIVERSITY. 



Those of us who live in large cities 

 realize how difficult it is to follow our 

 favorite pastime of watching the stars. 

 The tall buildings forming the "sky- 

 line" of New York, so interesting to 

 see from the harbor, decrease to such 

 an extent the line of the sky visible 

 that a resident of Manhattan can ob- 

 serve the heavenly bodies only when 

 they are comparatively near the zenith. 

 In addition, the street lights shining 

 on the dust of the city illuminates the 

 sky so that we can view only the moon, 

 planets and brighter stars. The people 

 of Chicago or Pittsburgh are not bet- 

 ter situated, for if their buildings are 

 not so high, their atmospheres (from 

 the use of soft coal), however, are not 

 so clear. The vast majority of the 

 readers of these lines do not live in 

 large cities, and consequently they are 

 able to watch the skies, which in the 

 early evenings at this time of year are 

 probably more interesting than at any 

 other season of the year. 



Those who watch the rising of the 

 moon in these ear!)'- fall months cannot 

 but help notice the difference which 

 years and years ago caused the pious 

 farmers to thank the all-wise Creator 

 for causing the full moon to rise at 

 nearly the same time for several nights 

 in succession, thus giving additional 

 light for harvesting the crops. The 

 Harvest Moon is the full moon which 

 falls nearest the Autumnal Equinox, 

 and in 1910. occurred on September 18. 

 The Hunter's Moon is in the follow- 

 ing month, and comes on October 18. 



It is surprising that so few people 

 know the exact cause of these pecu- 

 liarities of the moon ; but a little 



thought will readily explain them. As 

 everyone knows, the moon is moving 

 eastwards in her orbit round the earth, 

 and consequently rises later each night. 

 On the average this amounts to about 

 fifty minutes. By consulting any 

 "patent medicine" almanac, however, 

 it will be seen at a glance that the 

 moon does not rise each night fifty 

 minutes later, but that the intervals be- 

 tween successive nights vary enor- 

 mously at different times of the month. 

 A similar feature is also seen in the 

 times of sunrise caused by the sun 

 apparently moving once a year about 

 the earth in the ecliptic, inclined 23% 

 degrees to the equator. The variation 

 in the times of sunrise and sunset, and 

 the march of the seasons in conse- 

 quence, we are all familiar with. 



The moon revolves about the earth 

 nearly in the plane of the ecliptic also, 

 the time of her revolution is a month 

 and not a year, and so each month goes 

 through her variation of rising and set- 

 ting, as can be seen by consulting the 

 afore-mentioned almanac. In each 

 month there is a least variation in the 

 time of moonrise; but only in the au- 

 tumn months does this come near the 

 time of full moon. As w r e ordinarily 

 notice the time of rising of the moon, 

 only when it is near the full — when it 

 rises at sunset — the Harvest Moon, be- 

 fore the days of congested rural life 

 and electric lights, came to be a mark- 

 ed phenomenon. 



Rut not only does the Harvest and 

 Hunter's moons rise at nearly the same 

 hours for several nights, but they rise 

 farther and farther north of east. The 

 reasons may be visualized with great 

 readiness by getting a hollow rubber 

 ball three inches in diameter and stick- 

 ing a knitting needle through it. Mark 



