Other Stars and Constellations 207 



covered to have a companion that revolves around it 

 in about 40 years. 



The Twins. North of Canis Minor and northeast 

 of Orion is the constellation Gemini, the Twins. Their 

 heads are marked by two bright stars, Castor and Pollux, 

 about 4^ degrees apart, and their bodies by two parallel 

 lines of stars extending toward Orion. A line drawn 

 from Polaris to Procyon would pass between Castor 

 and Pollux. This constellation is crossed by the ecliptic 

 and is one of the twelve constellations of the zodiac. 

 Castor and Pollux are interesting for several reasons. 

 Some three centuries ago, when Greek letters were as- 

 signed to the stars in Gemini, Castor was called Alpha, 

 and Pollux, Beta; but as Pollux, which is south and 

 east of Castor, is now the brightest in the constellation, 

 they are thought to have changed in brightness. Being 

 farther north than the bright stars previously mentioned 

 in this chapter, they remain longer above the horizon 

 and may be seen in the evening from November till 

 June. In spring they are west of the meridian, or plane 

 which passes through the zenith from north to south. 

 They were supposed by the ancients to have a favorable 

 influence over navigation and were often represented in 

 the figureheads of ships. 



Double stars. Castor is what astronomers know 

 as a binary or double star. So close to it that you can- 

 not distinguish it is a star bright enough to be easily 

 seen without a telescope, if it were not near any other 

 star. The two are not only apparently near when seen 

 with a telescope, but, as was discovered about 200 years 

 ago, are really associated, although in all that time they 



