8 90 Handbook of Nature-Study 



any more than the figure on the blackboard has to do with the pointer; it 

 simply happens to lie in the direction toward which the northern end of the 

 earth's axis points. In the southern skies, there is no convenient star which 

 lies directly above the South Pole, so there is no South Pole-star. It is also 

 a coincidence that the needle of the mariner's compass points toward the 

 North Star; the earth being a large magnet exercises its influence on all 

 substances which can be magnetized, and since the poles of our great earth- 

 magnet are nearly in line with the poles of the earth's axis, the magnetic 

 needle naturally points north and south, and the North Star chances to be 

 nearly in the direction toward which the northern end of the compass needle 

 points. 



The Pole-star cannot be seen from the southern hemisphere ; but if we 

 should start from Florida, on a journey toward Baffin's Bay, we should 

 discover that each night this star would seem higher in the sky. And if we 

 should succeed in reaching the North Pole, we would find the Pole-star 

 directly over our heads, and what a wonderful sight the stars would be from 

 this point ! For none of the stars which we could see would rise or set, but 

 would move around us in circles parallel to the horizon. 



The Big Dipper points towards the Pole-star, and to us seems to revolve 

 around it every twenty-four hours but, of course, this appearance is caused 

 by the fact that we ourselves are revolving from west to east. Therefore, 

 the stars seems to revolve from west to east under the Pole-star and from 

 east to west above it, or in exactly the opposite direction in which the 

 hands of a clock turn. Owing to the movement of the earth in its orbit, the 

 Big Dipper and all the other stars arrive at a certain point in our sky four 

 minutes earlier each day or about two hours earlier each month; thus, the 

 Big Dipper is east of the Pole-star with handle down in the evenings of 

 January, while at the same time of night in July, it is west of the Pole-star 

 with the handle up. But the time of year that a certain star reaches a cer- 

 tain point is so invariable, that if we know star time, or sidereal time as it is 

 called, we can tell just what hour of the night it is when a star passes this 

 point. Thus, the Big Dipper and the other polar constellations are the 

 night clock of the sailors of the northern hemisphere; for though this great 

 polar clock has its hands moving around the wrong way, it gains time 



with such regularity that anyone 

 who understands is able to compute 

 exact time by it. 



The Little Dipperliesmuchnearer 

 the Pole-star than does the Big Dip- 

 per; in fact, the Pole-star itself is 

 the end ')f the handle of the Little 

 Dipper. Besides the Pole-star, there 

 are two more stars in the handle 

 of the Little Dipper, and of the four 

 stars which make the bowl, the two 

 that form the outer edge are much 

 the brighter. The bowl of the Little 

 Dipper is above or below the Pole- 

 star according to the hour of the 

 evening, or the night of the year, for 

 it apparently revolves about the 

 The Pole-star and the Big and Little Dippers. Pole-.star as does the Big Dipper. 



