one, and it appears that the seven
principal stars have not changed in this lapse of time to any large
extent, so that the configuration of the Great Bear remains practically
the same now as it was then. The beginner must first obtain an
acquaintance with this group of seven stars, and then his further
progress in this branch of astronomy will be greatly facilitated. The
Great Bear is, indeed, a splendid constellation, and its only rival is
to be found in Orion, which contains more brilliant stars, though it
does not occupy so large a region in the heavens.

[Illustration: Fig. 80.--The Great Bear and Pole Star.]

[Illustration: Fig. 81.--The Great Bear and Cassiopeia.]

In the first place, we observe how the Great Bear enables the Pole Star,
which is the most important object in the northern heavens, to be
readily found. The Pole Star is very conveniently indicated by the
direction of the two stars, b and a, of the Great Bear, which
are, accordingly, generally known as the "pointers." This use of the
Great Bear is shown on the diagram in Fig. 80, in which the line b
a, produced onwards and slightly curved, will conduct to the Pole
Star. There is no likelihood of making any mistake in this star, as it
is the only bright one in the neighbourhood. Once it has been seen it
will be readily identified on future occasions, and the observer will
not fail to notice how constant is the position which it preserves in
the heavens. The other stars either rise or set, or, like the Great
Bear, they dip down low in the north without actually setting, but the
Pole Star exhibits no considerable changes. In summer or winter, by
night or by day, the Pole Star is ever found in the same place--at
least, so far as ordinary observation is concerned. No doubt, when we
use the accurate instruments of the observatory the notion of the fixity
of the Pole Star is abandoned; we then see that it has a slow motion,
and that it describes a small circle every twenty-four hours around the
true pole of the heavens, which is not coincident with the Pole Star,
though closely adjacent thereto. The distance is at present a little
more than a degree, and it is gradually lessening, until, in the year
A.D. 2095, the distance will be under half a degree.

The Pole Star itself belongs to another inconsiderable group of stars
known as the Little Bear. The two principal members of this group, next
in brightness to the Pole Star, are sometimes called the "Guards.