14 A Short History of Astronomy 



arose twelve zodiacal constellations, the nam.s of which 

 have come down to us with unimportant changes from 

 early Greek times.* Owing, however, to an alteration of 

 the position of . the equator, and consequently of the 

 equinoctial points, the sign Aries, which was defined by 

 Hipparchus in the second century B.C. (see chapter n., 42) 

 as beginning at the vernal equinoctial point, no longer 

 contains the constellation Aries, but the preceding one, 

 Pisces ; and there is a corresponding change throughout 

 the zodiac. The more precise numerical methods of 

 modern astronomy have, however, rendered the signs of 

 the zodiac almost obsolete ; but the first point of Aries ( r ), 

 and the first point of Libra (==), are still the recognised 

 names for the equinoctial points. 



In some cases individual stars also received special 

 names, or were called after the part of the constellation in 

 which they were situated, e.g. Sirius, the Eye of the Bull, 

 the Heart of the Lion, etc. ; but the majority of the present 

 names of single stars are of Arabic origin (chapter in., 64). 



14. We have seen that the stars, as a whole, retain 

 invariable positions on the celestial sphere,t whereas the 

 sun and moon change their positions. It was, however, 

 discovered in prehistoric times that five bodies, at first 

 sight barely distinguishable from the other stars, also changed 

 their places. These five Mercury, Venus, Mars, Jupiter, 

 and Saturn with the sun and moon, were called planets, \ 

 or wanderers, as distinguished from the fixed stars. 



* The names, in the customary Latin forms, are : Aries, Taurus, 

 Gemini, Cancer, Leo, Virgo, Libra, Scorpio, Sagittarius, Capricorn us, 

 Aquarius, and Pisces ; they are easily remembered by the doggerel 

 verses : 



The Ram, the Bull, the Heavenly Twins, 

 And next the Crab, the Lion shines, 



The Virgin and the Scales, 

 The Scorpion, Archer, and He-Goat, 

 The Man that bears the Watering-pot, 



And Fish with glittering tails. 



f This statement leaves out of account small motions nearly or 

 quite invisible to the naked eye, some of which are among the most 

 interesting discoveries of telescopic astronomy ; see, for example, 

 chapter x., 207-215. 



\ The custom of calling the sun and moon planets has now died 

 out, and the modern usage will be adopted henceforward in this 

 book. 



