Under the most favorable conditions Saturn can never
be nearer than 744,000,000 miles to the earth, or eight times the sun's
distance from us. It receives from the sun about one ninetieth of the
light and heat that we get.
[Illustration: SATURN IN ITS THREE PRINCIPAL PHASES AS SEEN FROM THE
EARTH. From a drawing by Bond.]
Saturn takes twenty-nine and a half years to complete a journey about
the sun. Like Jupiter, it rotates very rapidly on its axis, the period
being ten hours and fourteen minutes. Its axis of rotation is inclined
not far from the same angle as that of the earth's axis (26 deg.
49 min.), so that its seasons should resemble ours, although their
alternations are extremely slow in consequence of the enormous length
of Saturn's year.
Not including the rings in the calculation, Saturn exceeds the earth in
size 760 times. The addition of the rings would not, however, greatly
alter the result of the comparison, because, although the total surface
of the rings, counting both faces, exceeds the earth's surface about 160
times, their volume, owing to their surprising thinness, is only about
six times the volume of the earth, and their mass, in consequence of
their slight density, is very much less than the earth's, perhaps,
indeed, inappreciable in comparison.
Saturn's mean diameter is 73,000 miles, and its polar compression is
even greater than that of Jupiter, a difference of 7,000 miles--almost
comparable with the entire diameter of the earth--existing between its
equatorial and its polar diameter, the former being 75,000 and the
latter 68,000 miles.
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