CHAPTER VI 



THE SOLAR SYSTEM AND UNIVERSE 



126. The Solar System. The Sun and Moon are not 

 the only celestial bodies which pass between our eyes and 

 the dome of stars. Several bright objects, which, unlike 

 the stars, shine without twinkling by light reflected from 

 the Sun and show a distinct disc in the telescope, were 

 long ago called planets^ or wanderers, for they pursue a 

 devious track among the constellations, changing in posi- 

 tion on the star-dome from night to night. All the planets 

 are related to each other, as their wanderings are all 

 confined to the belt of sky termed the zodiac, extending 

 only a few degrees on each side of the ecliptic. The 

 distances of these bodies from the Earth have been 

 measured, and it has been proved that like the Earth 

 they all rotate and revolve round the Sun in elliptical 

 orbits, the planes of which are, as a rule, only slightly 

 inclined to the plane of the ecliptic. Some of the statistics 

 of the members of the solar system are given in the following 

 table. 



127. Inner Planets. The four planets next the Sun 

 are often called the inner planets. Mercury and Venus 

 are never seen very far from the Sun, and Mercury is 

 rarely visible to the naked eye. Venus, visible sometimes 

 as the evening star shortly after sunset, and at other times 

 as the morning star shortly before sunrise, is a magnificent 

 object, its light being often strong enough to throw a 

 distinct shadow. These two planets exhibit phases like 



