omets--The Planets are illuminated by the Sun--The
Stars are not--The Earth is really a Planet--The Four Inner
Planets, Mercury, Venus, the Earth, and Mars--Velocity of the
Earth--The Outer Planets, Jupiter, Saturn, Uranus, Neptune--Light
and Heat received by the Planets from the Sun--Comparative Sizes of
the Planets--The Minor Planets--The Planets all revolve in the same
Direction--The Solar System--An Island Group in Space.

In the two preceding chapters of this work we have endeavoured to
describe the heavenly bodies in the order of their relative importance
to mankind. Could we doubt for a moment as to which of the many orbs in
the universe should be the first to receive our attention? We do not now
allude to the intrinsic significance of the sun when compared with other
bodies or groups of bodies scattered through space. It may be that
numerous globes rival the sun in real splendour, in bulk, and in mass.
We shall, in fact, show later on in this volume that this is the case;
and we shall then be in a position to indicate the true rank of the sun
amid the countless hosts of heaven. But whatever may be the importance
of the sun, viewed merely as one of the bodies which teem through space,
there can be no hesitation in asserting how immeasurably his influence
on the earth surpasses that of all other bodies in the universe
together. It was therefore natural--indeed inevitable--that our first
examination of the orbs of heaven should be directed to that mighty body
which is the source of our life itself.

Nor could there be much hesitation as to the second step which ought to
be taken. The intrinsic importance of the moon, when compared with other
celestial bodies, may be small; it is, indeed, as we shall afterwards
see, almost infinitesimal. But in the economy of our earth the moon has
played, and still plays, a part second only in importance to that of the
sun himself. The moon is so close to us that her brilliant rays pale to
invisibility countless orbs of a size and an intrinsic splendour
incomparably greater than her own. The moon also occupies an exceptional
position in the history of astronomy; for the law of gravitation, the
greatest discovery that science has yet witnessed, was chiefly
accomplished by observations of the moon. It was therefore natural that
an early chapter in our Story of the Heavens should be devoted to a body
the interest of which approximated so closely to that o