Astronomy Explained Upon Sir Isaac Newton's Principles: And made easy to those who have not studied mathematicsFerguson, James
Science
Astronomy Explained Upon Sir Isaac Newton's Principles: And made easy to those who have not studied mathematics
Ferguson, James
Astronomy -- Early works to 1800
80. To Saturn, the Sun appears only 1/90th part so big as to us; and the
light and heat he receives from the Sun are in the same proportion to
ours. But to compensate for the small quantity of sun-light, he has five
Moons, all going round him on the outside of his Ring, and nearly in the
same plane with it. The first, or nearest Moon to Saturn, goes round him
in 1 day 21 hours 19 minutes; and is 140 thousand miles from his center:
The second, in two days 17 hours 40 minutes; at the distance of 187
thousand miles: The third, in 4 days 12 hours 25 minutes; at 263
thousand miles distance: The fourth, in 15 days 22 hours 41 minutes; at
the distance of 600 thousand miles: And the fifth, or outermost, at one
million 800 thousand miles from Saturn’s center, goes round him in 79
days 7 hours 48 minutes. Their Orbits in the Scheme of the Solar System
are represented by the five small circles, marked 1. 2. 3. 4. 5. on
Saturn’s Orbit; but these, like the Orbits of the other Satellites, are
drawn fifty times too large in proportion to the Orbits of their Primary
Planets.
[Sidenote: His Axis probably inclined to his Ring.]
81. The Sun shines almost fifteen of our years together on one side of
Saturn’s Ring without setting, and as long on the other in it’s turn. So
that the Ring is visible to the inhabitants of that Planet for almost
fifteen of our years, and as long invisible by turns, if it’s Axis has
no Inclination to it’s Ring: but if the Axis of the Planet be inclined
to the Ring, suppose about 30 degrees, the Ring will appear and
disappear once every natural day to all the inhabitants within 30
degrees of the Equator, on both sides, frequently eclipsing the Sun in a
Saturnian day. Moreover, if Saturn’s Axis be so inclined to his Ring, it
is perpendicular to his Orbit; and thereby the inconvenience of
different seasons to that Planet is avoided. For considering the length
of Saturn’s year, which is almost equal to thirty of ours, what a
dreadful condition must the inhabitants of his Polar regions be in, if
they be half of that time deprived of the light and heat of the Sun?
which must not be their case alone, if the Axis of the Planet be
perpendicular to the Ring, but also the Ring must hide the Sun from vast
tracks of land on each side of the Equator for 13 or 14 of our years
together, on the south side and north side by turns, as the Axis
inclines to or from the Sun: the reverse of which inconvenience is
another good presumptive proof of the Inclination of Saturn’s Axis to
it’s Ring, and also of his Axis being perpendicular to his Orbit.
[Sidenote: How the Ring appears to Saturn and to us.
In what Signs Saturn appears to lose his Ring; and in what
Signs it appears most open to us.]
Public-domain text, read in full here on John Shaqi.
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