22 
THE GUIDE TO NATURE 
earth changes its axis of rotation. At 
present the axis lies in the direction of 
the north star (Polaris), E, Figure i, 
but it was not always so and will not 
always be so. The pole moves in a 
circle of radius twenty-three and one- 
half degrees about a center at C (Fig- 
which we now see, including Sirius, the 
brightest of all the stars, and a portion 
of the constellation Orion. The summer 
constellations now will be winter con- 
stellations then and vice versa. The 
north pole of the sky is now about 
seven minutes closer to the pole star 
ure i). The circle is shown in Figure 
2. The complete motion in this circle 
requires about 26,000 years. The axis 
will be farthest from its present posi- 
tion in half of this period or 13,000 
years, when Vega at D. Figure 1, will 
be the bright star closest to the pole 
but by no means as close to the pole 
as our present pole star. At that time 
Polaris applied to the present pole star 
will be an anachronism. 
This motion of the axis makes slow 
but sure changes in the apparent posi- 
tions of the stars. In 13,000 years our 
present pole stars will be forty-eight 
degrees from the pole, moving about 
it much as Vega now does. The dip- 
pers would hardly be called circum- 
polar constellations. We should then 
be able to see the star nearest to the 
sun, Alpha Centauri. and the Southern 
Cross, but we would not be able to see 
some of the choicest portions of the sky 
than it was in 1900. The difference, 
which is now sixty-seven minutes, will 
be reduced to its smallest amount, 
about thirty minutes, in two hundred 
years. After that the two separate. 
When this motion was discovered in 
125 B. C. the pole was twelve degrees 
from the present pole star. 
All of these motions and a number 
of others are caused by motions of the 
earth and are not motions of the stars 
themselves. The stars change their 
positions by very small amounts due to 
motions of the stars themselves, but 
these motions are so very slow that 
very long periods of time are necessary 
before the change could be seen with 
the naked eve. 
How matchless Nature’s beauties! 
How blind unseeing eyes! 
From out our lives, how tragic 
So much to sacrifice! 
— Emma Peirce. 
