136 FROM NEBULA TO NEBULA 



THE SOLAR ORBIT 



EXPLANATION: On account of the immense disparity in 

 the dimensions, it is impossible to draw this figure to scale. 

 Its purpose is to illustrate the relation of the earth's axial 

 inclination and her general movements with reference to the 

 sun and his orbit. The large circle is, of course, the Ant- 

 arctic Circle of our Gravisphere and represents the sun's 

 path, or rather the path of the center of gravity of his 

 system. The next smaller circle denotes the orbit of the 

 earth, but relatively enormously magnified. Arrow-heads in 

 all the circles indicate the direction of movement. The 

 positions A, A 1 , A 2 , A 3 show the earth at the instant of her 

 vernal equinox, B, B 1 , B 2 , B 3 at our summer solstice, and so 

 on. The celestial point of vernal equinox is found by sight- 

 ing through the center of the sun from the center of the 

 earth at the positions A, A 1 , A 2 , A 8 . Unfortunately, however, 

 owing to the fact that the sun's center is less steady in its 

 course than the center of gravity of his system, the data of 

 observation are not as consistent as they otherwise would be. 

 The letter C denotes the center (Centrum) of the solar orbit 

 and V the Vertex, the latter, however, needing to be pictured, 

 not in the plane of the paper but about five inches behind it. 

 Here the orbit is shown as a closed curve, whereas in reality 

 it is a spiral. To obtain the correct conception the book 

 should be held horizontally and then slowly lowered away 

 from the eye, at the same time imagining the rotatory move- 

 ments as in progress. Note that our view is from a point 

 south of the ecliptic. 



