212 



THE GUIDE TO NATURE 



not be until toward the close of April 

 that the western edge of Taurus will 

 have reached the western horizon and 

 the withdrawal of the bright winter 

 groups from our evening heavens will 

 begin. 



The remarkable position of the planet 

 lupiter, almost in the center of Taurus 



Figure 2. South Polar regions of the earth, show- 

 ing the area within which the eclipse of the sun of 

 December 14 will be visible. 



and just above the Hyades, will afford 

 the observer an unusually good oppor- 

 tunity for clearly seeing the motion of 

 this slowly moving world. Though 

 Jupiter moves slowly eastward in its 

 great orbit and thus completes the en- 

 tire circuit of the heavens in the course 

 of twelve years, it is now "retrograd- 

 ing," or moving westward, among the 

 stars. This apparent backward motion 

 is caused by the fact that our earth, 

 which is now between Jupiter and the 

 sun, is moving eastward faster than 

 the distant planet and so displacing it 

 westward in the sky. 



On December i the observer will 

 see Jupiter at the position of A of Fig- 

 ure i, wholly to the east of the Hyades, 

 while by the end of the month it will 

 have moved to the position B, wholly 

 to the west of this group and almost 

 midway between the Pleiades and the 

 star at C. This backward motion will 

 continue until next January 26, when 

 a rapid eastward motion will begin. 

 ***** 



The Eclipses of December. 



Two interesting eclipses will occur 

 during the present month, one of the 

 sun and one of the moon. These will 

 make a total of no less than seven eclip- 



ses which have taken place during the 

 year 10 17. which is the greatest number 

 that can occur in any one year. 



The first December eclipse will be a 

 so-called "Annular Eclipse" of the sun. 

 This will be wholly invisible to us and 

 can, in fact, only be seen by observers 

 within the area M, N, P, Q of Figure 

 2. Throughout most of this region the 

 black disk of the moon will be seen to 

 move across and so cover a portion 

 only of the bright disc of the sun ; from 

 all points along the line A, B however 

 the center of the moon will be seen to 

 move exactly across the center of the 

 sun. At this time our satellite will be 

 so far from the earth that it will not ap- 

 pear sufficiently large to completely 

 hide the sun. Even when the center of 

 the moon is seen exactly upon the cen- 

 ter of the sun, a narrow rim of the sun's 

 disc will remain uncovered, thus en- 

 circling the black disc of the moon 

 with a brilliant ring of light. 



The second December eclipse will 

 be a total eclipse of the moon. This 

 may be viewed during the early morn- 

 ing hours of December 28 from all sta- 

 tions in North and South America and 

 from Eastern Asia. Unfortunately, the 

 eclipse occurs at a rather inconvenient 

 hour; it will be necesary for the obser- 

 ver to remain up until long after mid- 

 night of December 27 in order to wit- 

 ness it, but the phenomena are so very 

 interesting that he will be well repaid 

 for his trouble. 



The great shadow of the earth, which 

 stretches out into space to a distance 

 of 857,000 miles in a direction exactly 

 opposite the sun, has a conical shape. 

 From any point within this shadow 

 cone the light of the sun will be cut 

 off, the brilliant sun's disc being hidden 

 as seen from this point by the opaque 

 ball of the earth coming in front of it. 

 The moon will plunge into this shadow 

 and so be darkened on December 28, 

 the center of the moon moving along 

 the path M, N of Figure 3. 



The moon's center will reach the 

 position A and the eclipse begin on 

 December 28 at 3.5.6 A. M. (Eastern 

 standard time) ; it will reach the posi- 

 tion B and the moon be most deeply im- 

 mersed in the shadow at 4.46.18 A. M., 

 and it will reach the point C and the 

 eclipse will end at 6.27.24 A. M. 



