ASTRONOMY 



87 



Ae eclipse of these moons, the motion of light 

 was ascertained ; and they are found to be of es 

 sential use in determining the longitude of places 

 on the surface of our globe. This planet, if seen 

 from its nearest moon, will present a surface a 

 thousand times as large as our moon does to us, 

 and will appear in the form of a crescent, a half- 

 moon, a gibbous phase, and a full-moon, in regu 

 lar succession, every 24 hours. Jupiter s axis 

 being nearly perpendicular to his ortJJt, he has no 

 sensible change of seasons, such as ve experi 

 ence on the earth. Were we placed on ^e sur 

 face of this planet, with the limited powers of 

 vision we now possess, our earth and moon 

 would entirely disappear, as if they were blotted 

 out from the map of creation ; and the inhabitants 

 of these regions must have much better eyes than 

 ours, if they know that there is such a globe as 

 the earth in the universe. 



The planet Saturn. This planet is 900 mil 

 lions of miles distant from the sun, being nearly 

 double the distance of Jupiter. Its diameter is 

 79,000 miles, and, consequently, it is more than 

 nine hundred times the bulk of the earth. It 

 takes 29 years to complete its revolution about 

 the sun: but its diurnal motion is completed in 

 ten hours and sixteen minutes ; so that the year 

 in this planet is nearly thirty times the length of 

 ours, while the day is shorter, by more than one- 

 half. The year, therefore, contains about twen 

 ty-five thousand one hundred and fifty days, or 

 periods of its diurnal rotation, which is equal to 

 10,759 of our days. Saturn is of a spheroidal 

 figure, or somewhat of the shape of an orange ; 

 his equatorial being more than six thousand miles 

 longer than his polar diameter. His surface, 

 like that of Jupiter, is diversified with belts and 

 dark spots. Dr. Herschel, at certain times, per 

 ceived five belts on his surface, three of which 

 were dark, and two bright. The dark belts had 

 a yellowish tinge, and generally covered a larger 

 zone of the disk of Saturn, than the belts of Jupi 

 ter occupy upon his surface. On account of the 

 great distance of this planet from the sun, the 

 light it receives from that luminary is only the 

 ninetieth part of what we enjoy ; but, by calcula 

 tion, it is found, that this quantity is a thousand 

 times greater than the li^ht which the full moon 

 affords to us. Besides, it is surrounded by no 

 fewer than seven moon^, which supply it with 

 light in the absence of the sun. Five of these 

 inoons were discovered during the seventeenth 

 century, by Huygens and Cassini ; and the sixth 

 and seventh were discovered by Dr. Herschel, in 

 1789, soon after his large forty feet reflecting 

 Islescope was constructed. These moons, and 

 also those which accompany Jupiter, are esti 

 mated to be not less than the earth in magnitude, 

 and are found, like our moon, to revolve round 

 the: 1 - axis in the same time in which they revolve 

 about their rep&amp;lt;ictive primaries. 



Rings of Saturn. The most extraordinary 



circumstance connected with this planet, is, 

 the phenomenon of a double ring, which sur 

 rounds its body, but no where touches it, being 

 thirty thousand miles distant from any part ol 

 the planet, and is carried along with the planet 

 in its circuit round the sun. This is the most 

 singular and astonishing object in the whole range 

 of the planetary system ; no other planet being 

 found environed with so wonderful an appendage ; 

 and the planets which may belong to other sys 

 tems, being placed beyond the reach of our ob 

 servations, no idea can be formed of the peculiar 

 apparatus with which any of them may be fur 

 nished. This double ring consists of two con 

 centric rings, detached from each other ; the in 

 nermost of which is nearly three times as broad as 

 the outermost. The outside diameter of the exte 

 rior ring is 204,000 miles ; and, consequently, its 

 circumference will measure six hundred and 

 forty thousand miles, or eighty times the diame 

 ter of our globe. Its breadth is 7,200 miles, or 

 nearly the diameter of the earth. Were four 

 hundred and fifty globes, of the size of the earth, 

 placed close to one another, on a plane, this 

 immense ring would enclose the whole of them, 

 together with all the interstices, or open spaces 

 between the different globes. The outsioe dia 

 meter of the innermost ring is 184,000 miles, and 

 its breadth twenty thousand miles, or about 2$ 

 times broader than the diameter of the earth. 

 The dark space, or interval, betwoen the two 

 rings, is 2,800 miles. The breadth of both the 

 rings, including the dark space between them, 

 is thirty thousand miles, which is equal to the 

 distance of the innermost ring from the body of 

 Saturn. 



The following figure represents a view of Sa 

 turn and his rings, as they would appear, were 

 our eye perpendicular to one of the planes of those 

 rings ; but our eye is never so much elevated 

 above either plane, as to have the visual ray 

 standing at right angles to it ; it is never ele 

 vated more than 30 degrees above the planes of 

 the rings. When we view Saturn through a 

 telescope, we always see the ring at an oblique 

 angle, so that it appears of an oval form, the 

 outward circular rim being projected into an 

 ellipsis more or less oblong, according to the 

 different degrees of obliquity with which it is 

 viewed, as will be seen in the figure of Saturn 

 in the copperplate engraving. 



These rings cast a deep shadow upon the 

 planet, which proves that they are not shining 

 fluids, but composed of solid matter. They ap 

 pear to be possessed of a higher reflective power 

 than the surface of Saturn ; as the light re 

 flected by them is more brilliant than that of 

 the planet. One obvious use of this double ring 

 is, to reflect light upon the planet, in the absence 

 of the sun; what other purposes it may be in 

 tended to subserve, in the system of Saturn, is, 

 at present, to us unknown. The sun illuminates 



