2NN 



THE GUIDE TO NATURE 



wh.it distance ii is possible for the 

 mi ii in tn be En mi the m »de i >f her i »rbi1 

 and still have an eclipse take place, 

 Since the m< »1 ii in i >i" the mi n in is w ell 

 known to the astronomer, it is possible 



For him to calculate many years ill ad 

 \ ance the time at which an eclipse i <i 

 the sun or moon will take place. In a 

 remarkable German book by < >ppolzer, 

 there is given the elements of all the 

 eclipses which occur for the next two 

 hundred and lift\ years, and by a 

 glance at a map one ran tell where to 

 travel in order to see an) eclipse of the 

 sun during thai interval. Xot only can 

 the astronomer by his calculations see 

 into the future in such a remarkable 

 way. but lie can look back into the dim 

 and mist} past, and this same both tells 

 when and where all eclipses have taken 

 place during the past thirty centuries, 

 b i the date 1207 B. C. 



The accuracy of astronomic predic- 

 tion in the case of Halley's comet caus- 

 ed all to wonder at the exactness of the 

 grand old science of astronomy, but 

 eclipses can be foretold with a pre- 

 cisii hi far greater. 



Since the moon moves in her orbit 

 in an easterly direction, it overtakes 

 the shadow of the earth and a darken- 

 ing appears first on the eastern edge 

 of the moon. The appearance of the 

 moon as it crosses through the shadow 

 is well shown by the diagram above. 

 At 5.44 ]). m. Eastern Standard time, 

 the moon enters the shadow- and the 

 eclipse begins. For the next hour and 

 eleven minutes, more and more of the 

 moon's light is cut off and at 6.55 the 

 eclipse becomes total. The middle of 

 the eclipse takes place at 7. 21 p. m. It 

 is then noticed that though the moon 

 has suffered an eclipse, there is still 

 light, the moon appears as a dull cop- 

 per color. This light in the earth's 

 shadow is covered by the bending or 

 refraction of the sun's rays by the at- 

 mosphere of the earth. The sun or 

 moon appear red to us when in the 

 horizon, rising or setting, because the 

 atmosphere has robbed the white light 

 of all but its red rays. In passing round 

 to the moon at the time of its eclipse, 

 the sun's light has to 1 ass again 

 through a great layer c; : tmosphere 



with the result that the moon appears 

 a \ iiy deep red. 



The eclipse of November 16 is not a 



long one, totality lasts for less than an 

 hour, and at 7.47 p. m. the moon be- 

 gins to emerge from the shadow and 

 the eclipse is over at 8.58. The whole 

 eclipse from beginning to end lasts a 

 little more than three hours. 



The eclipses of the moon are unin- 

 teresting compared with eclipses of the 

 sun. At the latter eclipse, when total, 

 the magnificent corona appears, the 

 most gorgeous of all natural phenom- 

 ena. There are then many vital prob- 

 lems about the sun that the astronomer 

 is anxious to solve, and so eclipse ex- 

 peditions are a very important part of 

 solar research. The writer has trav- 

 eled about thirty-hve thousand miles 

 in observing such phenomena. Re- 

 garding the moon there are few ques- 

 tions left to solve, and the fact that the 

 moon passes into a shadow is generally 

 of little interest to the average prac- 

 tical astronomer. In fact, it might 

 even be said that most professional as- 

 tronomers would prefer to have the 

 moon perpetually eclipsed, for then 

 many added hours could be given to 

 the photography of the sky — with 

 which the moon interferes by fogging 

 the plates. 



The moon during an eclipse has been 

 photographed repeatedly, the best re- 

 sults perhaps being those obtained by- 

 Professor E. E. Barnard. If the moon 

 has a small satellite — which is not im- 

 possible — it will be detected in this 

 way. A photograph of such an eclipse 

 renders evident that the moon is mov- 

 ing eastwards among the stars, and the 

 length of the exposure given would 

 make it plain that the moon is moving 

 its own diameter in an hour. 



In the diagram above the moon and 

 shadow are drawn to scale and repre- 

 sent exactlv the appearance of the 

 eclipse. One must not be confused 

 with the position of the north. This 

 has no reference whatever to the hori- 

 zon, near which the moon will be when 

 the eclipse begins, for north is the 

 direction towards the north pole of the 

 heavens, or the North Star. On the 

 diagram is also marked the times at 



