phere, in the
constellation of Pictor. Nothing, indeed, better shows the enormous
distance of the stars from us, and the consequent inability of even such
rapid movements to alter the appearance of the sky during the course of
ages, than the fact that it would take more than two centuries for the
star in question to change its position in the sky by a space equal to
the apparent diameter of the moon; a statement which is equivalent to
saying that, were it possible to see this star with the naked eye, which
it is not, at least twenty-five years would have to elapse before one
would notice that it had changed its place at all!

Both the stars just mentioned are very faint. That in Pictor is, as has
been said, not visible to the naked eye. It appears besides to be a very
small body, for Sir David Gill finds a parallax which makes it only as
far off from us as Sirius. The Groombridge star, too, is just about the
limit of ordinary visibility. It is, indeed, a curious fact that the
fainter stars seem, on the average, to be moving more rapidly than the
brighter.

Investigations into proper motions lead us to think that every one of
the stars must be moving in space in some particular direction. To take
a few of the best known. Sirius and Vega are both approaching our system
at a rate of about 10 miles per second, Arcturus at about 5 miles per
second, while Capella is receding from us at about 15 miles per second.
Of the twin brethren, Castor and Pollux, Castor is moving away from us
at about 4-1/2 miles per second, while Pollux is coming towards us at
about 33 miles per second.

Much of our knowledge of proper motions has been obtained indirectly by
means of the spectroscope, on the Doppler principle already treated of,
by which we are enabled to ascertain whether a source from which light
is coming is approaching or receding.

The sun being, after all, a mere star, it will appear only natural for
it also to have a proper motion of its own. This is indeed the case; and
it is rushing along in space at a rate of between ten and twelve miles
per second, carrying with it its whole family of planets and satellites,
of comets and meteors. The direction in which it is advancing is towards
a point in the constellation of Lyra, not far from its chief star Vega.
This is shown by the fact that the stars about the region in question
appear to be opening out slightly, while those in the contrary portion
of the sky appear similarly to b