Saturn has no less than five Satellites; the first, or innermost, revolves about him in 1 Day, and 21 Hours, at the distance of 4⅜ Semidiameters of ♄, from his center; the second compleats his period in 2¾ Days, at the distance of 5³/₅ of his Semidiameters; the third, in about 4½ Days, at the distance of 8 Semidiameters; the fourth performs its course in about 16 Days, at the distance of 18 Semidiameters; the fifth, and outermost, takes 79⅓ Days, to finish his course, and is 54 Semidiameters of Saturn distant from his center. The Satellites, as well as their primaries, perform their revolutions from West to East: The planes of the Orbits of the Satellites of the same Planet are variously inclined to one another, and consequently are inclined to the plane of the Orbit of their primary.
Saturn’s Ring.
Besides these attendants, Saturn is encompassed with a thin plain Ring, that does no where touch his body; The diameter of this Ring is to the diameter of Saturn, as 9 to 4; and the void space between the Ring and the body of Saturn is equal to the breadth of the Ring itself; so that in some situations the Heavens may be seen between the Ring and his body. This surprizing phænomenon of Saturn’s Ring, is a modern discovery; neither were the Satellites of Jupiter and Saturn known to the ancients. The Jovial Planets were first discovered by the famous Italian philosopher Galilæus, by a telescope which he first invented; and the celebrated Cassini, the French king’s astronomer, was the first that saw all the Satellites of Saturn; which by reason of their great distances from the Sun, and the smallness of their own bodies, cannot be seen by us, but by the help of very good glasses.
Annual Motion.
Diurnal Motion.
The motion of the primary Planets round the Sun (as also of the Satellites round their respective primaries) is called their Annual Motion; because they have one Year, or alteration of Seasons compleat, in one of these revolutions. Besides this annual motion, four of the Planets, viz. Venus, the Earth, Mars, and Jupiter revolve about their own Axis, from West to East; and this is called their Diurnal Motion. For by this rotation, each point of their surfaces is carried successively towards or from the Sun, who always illuminates the hemisphere which is next to him, the other remaining obscure; and while any place is in the hemisphere, illuminated by the Sun, it is Day, but when it is carried to the obscure hemisphere, it becomes Night; and so continues, until by this rotation the said place is again enlightened by the Sun.
Diurnal Motion of the ♁, ♀, ♂ and ♃.
☉ and ☽ likewise turn round their Axis.
The Earth performs its revolution round its axis in 23 Hours, 56 Minutes;[2] Venus, in 24 Days, 8 Hours; Mars, in 24 Hours, and 40 Minutes; and Jupiter moves round his own axis in 9 Hours, and 56 Minutes. The Sun also is found to turn round his axis from West to East, in 27 Days: And the Moon, which is nearest to us of all the Planets, revolves about her axis in a Month, or in the same space of time that she turns round the Earth; so that the Lunarians have but 1 Day throughout the Year.
The Planets are Opaque and Globular.