any known star.

It must not be supposed that these enormous velocities seem so to
us. Not one of them, even the greatest, would be visible to the
naked eye until after years of watching. On our finger-ring scale,
1830 Groombridge would be some ten miles and Arcturus thirty or
forty miles away. Either of them would be moving only two or three
feet in a year. To the oldest Assyrian priests Lyra looked much as
it does to us to-day. Among the bright and well-known stars
Arcturus has the most rapid apparent motion, yet Job himself would
not to-day see that its position had changed, unless he had noted
it with more exactness than any astronomer of his time.

Another unsolved problem among the greatest which present
themselves to the astronomer is that of the size of the universe
of stars. We know that several thousand of these bodies are
visible to the naked eye; moderate telescopes show us millions;
our giant telescopes of the present time, when used as cameras to
photograph the heavens, show a number past count, perhaps one
hundred millions. Are all these stars only those few which happen
to be near us in a universe extending out without end, or do they
form a collection of stars outside of which is empty infinite
space? In other words, has the universe a boundary? Taken in its
widest scope this question must always remain unanswered by us
mortals because, even if we should discover a boundary within
which all the stars and clusters we ever can know are contained,
and outside of which is empty space, still we could never prove
that this space is empty out to an infinite distance. Far outside
of what we call the universe might still exist other universes
which we can never see.