100 DAY AND NIGHT. 



They are said to be in opposition, when their longitudes 

 differ half a circle, or they are in opposite sides of the 

 heavens. 



Questions.— 1. What is the ecliptic ?— explain. 2. What is the 

 zodiac ? — explain. ^ What ia meani t>y tlie plane of the earth's orbit ? 

 4. What are nodes .'' 5. What are the divisions of the ecliptic .'' 6. 

 What are the celestial poles.'' 7. What is the celestial equator .-' 8. 

 How is the axis of the earth situated with regard to the plane of the 

 ecliptic.^ 9. What are the poles of the ecliptic .•* 10. What is the la- 

 titude of a heavenly body .^ 11. The longitude.'' 12. How is the 

 longitude of a heavenly body reckoned and stated ? 13. What exam- 

 ple is given .' 14. What is the declination of a heavenly body. 15. 

 Right ascension .'' 16. When are two planets said to be in conjunct 

 tion ? 17. In opposition ? [Note. The points at which the ecliptic 

 cuts the celestial equator are called the equinoctial points. Those two 

 points of the ecliptic farthest from the equator are called sol'stices. 

 Ap'ogec, that point of the orbit of the moon which is farthest from the 

 earth. Per'igee, that point which is nearest to the earth.] 18. Look 

 at fig. 40. and point out the ecliptic, zodiac, and signs of the zodiac. 



LESSON 45. 



Day and Night. 



Ver'nal, belonging to the spring. 



Intersect', to cut, to divide each other mutually. 



By the diurnal motion of the earth, the same phenomena 

 appear as if all the celestial bodies turned round it ; so that 

 in its rotation from west to east, when the sun or a star just 

 appears on the eastern side of the horizon, it is said to be 

 rising, and as the earth continues its revolution, it seems 

 gradually to ascend till it has reached its meridian ; here the 

 object has its greatest elevation, and begins to decline till it 

 set, or become invisible on the western side. In the same 

 manner the sun appears to rise and run his course to the 

 western horizon, where he disappears and night ensues, till 

 he again illuminate the same part of the earth in another 

 diurnal revolution. One half of the earth's surface is con- 

 stantly illuminated, and by the regular motion of the earth 

 on its axis, every place is successively brought into light and 

 immersed in darkness. If the axis of the earth were always 

 perpendicular to the plane of the ecliptic, the days would 

 every where be of the same length, and just as long as the 



