CHAPTER XXXVI 



THE SUN. 



MOTION OF THE SUN THE SEASONS CHARACTER OF THE SUN SUN- 

 SPOTS ZODIACAL LIGHT. 



SUPPOSE that we rise early in the morning we shall, as the reader will say 

 see the sun rise that is, he appears to us to rise as the earth rotates. By 

 the accompanying diagram (fig. 544) we can understand how Sol makes his 

 appearance, and how he comes up again ; not, it will be observed, after the 

 manner stated by the Irishman, who declared that the sun " went down, and ran 

 round during the night when nobody was looking." The earth rotates from 

 west to east, and so the sun appears to move from east to west. If we look 

 at the diagram we shall see that after rising at O, the sun advances towards 

 the meridian in an oblique arc to A, the highest or 

 culminating point midday. He then returns, de- 

 scending to W ; this path is the diurnal arc. At 

 Q similarly, during his passage in the nocturnal arc, 

 he reaches the lowest or inferior culmination. ' H H 

 is the meridian. 



On the 2 1st of March, this path brings the sun 

 on the " equinoctial " line mentioned at the close 'of 

 the last chapter. Day and night are then of equal 

 duration as the arcs are equal. So this is the Vernal 

 (or spring) Equinox. Some weeks after the sun is 



at midday higher up at s', so the diurnal arc being longer, the day is longer. 

 (Z is the zenith, z' is the nadir, P p' is the celestial axis). From that time he 

 descends again towards the equinoctial to the autumnal equinox, and so on, 

 the diurnal arc becoming smaller and smaller until 

 the winter solstice is reached (s). 



From what has been previously said, it is evident 

 that the sun has a twofold apparent motion viz., 

 a circular motion obliquely ascending from the hori- 

 zon, which is explained by the rotation of the earth, 

 and by our position, o, to the earth's axis, pp' y and 

 also by a rising and setting motion between the 

 solstitial points, S and s', which causes the inequality 

 of the days and nights. Independently of the daily 

 motion of the sun, we observe that at the summer solstice, on the 2ist of 

 June, at midday, the sun is at s', and one half year later viz., on the 



Fig. 544. Sun's motion. 



Fig- 545- The ecliptic. 



