NOMENCLATURE. 



471 



\ 



now known accurately, and commented upon long before the event can 

 take place. 



We will close this chap- 



ii f l ._..?f.j_ '** ter by giving a brief expla- 



nation of the various defini- 

 tions most usually employed 

 in astronomy. 



1 . The Axis of the earth 

 is an imaginary line passing 

 through the centre (north and 

 south) ; the poles are the ex- 

 tremities of this line. 



2. The Equator is an 

 imaginary circle passing round 

 the globe, dividing it into 

 northern and southern hemi- 

 spheres. The equinoctial is 

 the plane of the former circle 

 extended to the heavens, and 

 when the sun appears in that 

 line the days and nights are 



A'' 1 



Fig. 499. The Zodiac. 



of equal duration twelve hours each. 



3. The Ecliptic is the sun's path through the heavens though, of 

 course, the sun does not actually move, and therefore the track, or supposed 

 circle, is really the earth's motion observable from the sun. When the moon 

 is near this circle eclipses happen. The ecliptic cuts the equinoctial at an 

 angle of about 2 3. One half is to the north and the other to the south of 

 the equinoctial. 



4. The Zodiac is a girdle extending 8 on each side of the ecliptic, in 

 which space of 16 the planets move. The zodiac is divided into twelve 

 parts of 30 each, called the " Signs." These names are as under written : 



NORTHERN SIGNS. 



Spring. Summer. 



Aries, the Ram, March. Cancer, the Crab, June. 



Taurus, the Bull, April. Leo, the Lion, July. 



Gemini, the Twins, May. Virgo, the Virgin, August. 



SOUTHERN SIGNS. 



Autumn. Winter. 



Libra, the Balance, September. Capricornus, the Goat, December. 



Scorpio, the Scorpion, October. Aquarius, the Waterbearer, January. 



Sagittarius, the Archer, November. Pisces, the Fishes, February. 



5. Colures are two circles dividing the ecliptic into four equal parts, and 

 making the seasons. 



6. The Horizon is the boundary line of our vision, and is called the 



