7-t HE A YENS. 



Curta'tion. — The interval between a planet's distance from the 



siin and the curtate distance. 

 Cynosure. — A name of the constellation Ursa Minor, or the 



LesHcr Bear, which contains, in the tail, the pole-star by 



which mariners are guided. 

 Declina'tion. — The distance of any object from the celestial 



equator, either northward or southward. 

 Dichot'omy. — Tlie phase of the moon when she shows just 



half her di.sk. 

 Disk. — Tlie face or visible projection of a celestial body, usually 



predicated of the sun, moon, or planets ; but the stars have 



also apparent disks. 

 Eclipse'. — An obscuration or interception of the light of the 



sun, moon, or other luminous body. 

 Eclip'tic. — The great circle of the heavens which the sun 



appears to describe in his annual revolution. 

 Equa'tor. — The great circle of the sphere, equally distant from 



the two poles of the world, or having the same poles as 



the world. 

 E'quinox. — The precise time when the sun enters one of the 



equinoctial points, making the day and night of equal 



length. 

 Fac'ulae. — Certain spots sometimes seen on the sun's disk, 



which appear brighter than the rest of his surface. 

 Fixed Stars. — Those which retain the same or very nearly the 



same position with respect to each other. 

 Gal'axy. — The Milk3'-Way. 

 Gemini (Lat., the Twins). — The third sign or constellation in 



the zodiac, which the sun enters about the 21st of May. 

 Geocentric Par'allax. — The apparent change of a body's place 



that would arise from a change of the spectator's station 



from the surface to the centre of the earth. 

 Ha'lo. — A luminous circle, usually prismatically colored, round 



the sun or moon, and supposed to be caused by tlie refrac- 

 tion of light through crystals of ice in the atmosphere. 

 Heliocentric Par'allax. — The arc of a great circle of the 



celestial sphere, drawn from the heliocentric to the geocen- 

 tric place of a body. 

 Heliom'eter (Gr. hc/ios, the sun, and melrro, I measure). — ■ 



An instrument for measuring with exactness the apparent 



diameter of the sun, moon, planets, etc. 

 Horizon. — A circle touching the earth at the place of the 



