234 Trees, Stars, and Birds 



FIGS. 141 and 142. The upper row shows the relative sizes of the planets, the 



Tracing the ecliptic. The sun is always on the ecliptic. 

 If it were to leave a trail in the sky to show where it 

 had been, this trail would mark the ecliptic. In summer 

 the sun rises to the north of east, is high in the south 

 at noon, and sets north of west. In winter it rises 

 south of east, is not very high above the southern horizon 

 at noon, and sets south of west. As it leaves no trace, 

 we need to keep in mind the path it seems to follow in 

 order to locate the ecliptic. At night in winter the 

 part of the ecliptic we can follow across the sky is the 

 part which the sun traversed in the daytime in summer. 

 This part is higher above the southern horizon than that 

 part of the ecliptic which we are able to trace on a sum- 

 mer night. The moon is never more than 5 degrees and 

 8 minutes from the ecliptic. 



Why a planet's brightness changes. The planets, 

 unlike most of the stars, change in brightness. For 

 weeks or months a planet becomes less bright, then 

 gradually regains its brilliancy. This is due to several 



