Brahe in the year 1572.

(Page 291)]

On account of the curvature of the earth's surface, the height at which
the Pole Star is seen above the horizon at any place depends regularly
upon the latitude; that is to say, the distance of the place in question
from the equator. For instance, at the north pole of the earth, where
the latitude is greatest, namely, 90 deg., the Pole Star will appear
directly overhead; whereas in England, where the latitude is about 50
deg., it will be seen a little more than half way up the northern sky.
At the equator, where the latitude is _nil_, the Pole Star will be on
the horizon due north.

In consequence of its unique position, the Pole Star is of very great
service in the study of the constellations. It is a kind of centre
around which to hang our celestial ideas--a starting point, so to speak,
in our voyages about the sky.

According to the constellation figures, the Pole Star is in _Ursa
Minor_, or the Little Bear, and is situated at the end of the tail of
that imaginary figure (see Plate XIX., p. 292). The chief stars of this
constellation form a group not unlike the Plough, except that the
"handle" is turned in the contrary direction. The Americans, in
consequence, speak of it as the "Little Dipper."

Before leaving this region of the sky, it will be well to draw attention
to the second magnitude star [z] in the Great Bear (Zeta Ursae Majoris),
which is the middle star in the "handle" of the Plough. This star is
usually known as Mizar, a name given to it by the Arabians. A person
with good eyesight can see quite near to it a fifth magnitude star,
known under the name of Alcor. We have here a very good example of that
deception in the estimation of objects in the sky, which has been
alluded to in an earlier chapter. Alcor is indeed distant from Mizar by
about one-third the apparent diameter of the moon, yet no one would
think so!

On the other side of Polaris from the Plough, and at about an equal
apparent distance, will be found a figure in the form of an irregular
"W", made up of second and third magnitude stars. This is the well-known
"Cassiopeia's Chair"--portion of the constellation of _Cassiopeia_ (see
Plate XIX., p. 292).

On either side of the Pole Star, about midway between the Plough and
Cassiopeia's Chair, but a little further off from it than these, are the
constellations of _Auriga_ and _Lyra_ (see Plate XIX., p. 292). The
former constellation will be easily recog