108 ANSWERS TO PRACTICAL QUESTIONS 



If we square the period of any planet, expressed in years, 

 and extract the cube root of this product, the result will be the 

 mean distance from the sun, expressed in astronomical units, 

 i.e., in radii of the earth's orbit. Jupiter's period of 12 years 

 will give a result of 5.2028. 93,000,000 miles x 5.2028 = 483,- 

 860,400 miles. 



6. The latitude of Albany is 42 39' N. ; what is the 

 sun's meridian altitude at that place ivJien it is in the celes- 

 tial equator ? 



(See Astronomy, note, p. 27.) 



90- 42 39'= 47 21'. 



7. Wliat is the co-latitude of a place ? 



(See Astronomy, note, p. 27.) 



The co-latitude is the complement of the latitude. 



8. Wliafis the declination of the zenith of the place in 

 which you reside ? 



(See Astronomy, note, p. 27.) 



It equals the latitude. 



.9. Why are the stars generally invisible by day ? 



(See Astronomy, p. 25.) 



The stars would be visible in the day-time if it were not for 

 the atmosphere. Compare the description of a lunar sky, on 

 page 134 of the Astronomy. 



10. Why is the ecliptic so called ? 



(See Astronomy, note, p. 58.) 



11. Who first taught that the earth is round ? 



The discovery of the rotundity of the earth has been as- 

 cribed to Thales ; others attribute it to Aristotle. 



12. IVliat is Astrology ? 



A magic art that pretends to foretell events by means of 

 the stars. 



13. How can ive distinguish the fixed stars from the 



planets ? 



(See Astronomy, pp. 2 and 203.) 



