IN DESCRIPTIVE ASTRONOMY. 109 



14. How long ivas the Ptolemaic system accepted? 



It was taught in the schools for about 1400 years, or until 

 the time of Galileo the 17th century. 



15. In ivhat respect did the Copernican system, differ 

 from the one now received ? 



(See Astronomy, p. 14.) 



10. For what is Astronomy indebted to Galileo? To 

 Neivton ? 



Galileo discovered the structure of the moon ; the existence 

 of Jupiter's moons and their revolution around their primary ; 

 the stars of the milky way ; and the rotation of the sun on 

 its axis (as proved by the appearance of the spots). Newton 

 discovered the law of gravitation, and by means of it explained 

 the specific gravity of the planets, the cause of the tides, the 

 shape of the earth, the theory of precession of the equinoxes, 

 and the paths of the comets. Bead Brewster's Life of Newton; 

 also, Buckley's History of Natural Science. 



17. What is the amount of the obliquity of the ecliptic ? 



(See Astronomy, p. 29.) 



18. Define Zenith. Nadir. Azimuth. Altitude. Equi- 

 noctial. Right Ascension. Declination. Equinox. Eclip- 

 tic. Colure. Solstice. Polar distance. Zenith distance. 

 The Zodiacs 



These terms are defined under the various subjects on pp. 

 26-30 of the Astronomy. 



IV. If the H.A.of the sun be 8O\ state in ^vhat sign he 

 is then located. 16O. 28O. 



(See Astronomy, table on p. 31.) 



1 sign = 30. 80 would locate the sun in Gemini ; 160, in 

 Virgo ; 280, in Capricornus. 



2O. Why does the angle which the ecliptic makes with 

 the horizon vary ? 



(See Astronomy, p. 29.) 



The angle between the horizon and the celestial equator is 

 constant ; the ecliptic being oblique to the equator, the angle 

 that it makes with the horizon must vary as it revolves. 



