Mercury and Venus 



239 



For both these reasons she is 

 more often seen. Her bright- 

 ness is due also to the fact 

 that her surface reflects much 

 of the sunlight that strikes it, 

 just as light wall paper re- 

 flects more light than dark 

 wall paper. Venus is so bright 

 that she has often been seen 



in the daytime. When eve- FIG. 145. Venus showing crescent 

 . i r i i phase. Like the moon. Venus 



mng star, she may be plainly shows all phases from a narrow 

 seen after sunset where the crescent to a full disk. 

 sun was 2 or 3 hours before. 



For periods of several months you cannot see Venus 

 in the evening because she goes down below the horizon 

 before the sun does. She will then rise before the sun 

 and may be seen in the east early in the morning. When 

 changing from evening to morning star and, 9^ months 

 later, from morning to evening star, Venus is so near 

 the sun for a few weeks as to be invisible on account of 

 the superior light of the sun. Venus as evening star 

 will be farthest from the sun on July 4, 1919, February 

 i, 1921, and September 18, 1922, and as morning star 

 about 9^ months earlier or later than these dates. 



Venus is 67,000,000 miles from the sun. At times 

 she approaches to within 25,000,000 miles of the earth, 

 but her dark side is then toward us, for only the side 

 toward the sun is illuminated. Apparently the planet 

 is enveloped in clouds, so that no permanent markings 

 are visible even with large telescopes. Venus's year 

 is 225 days long. Like Mercury, the planet always 



