390

THE PLANET SATURN.

in comparison with the diameter of their primary, the nearestof Jupiter ’s moons is nearly twice as far away as the nearestof Saturn ’s.

From the nearest satellite, Saturn ’s disc would present amagnificent spectacle, its diameter subtending an angle ofabout 37°. Its disc would, therefore, appear to be about 5,000times as large as that of our Moon , or nearly 400 times as largeas that which the Earth would present if seen from the Moon .From the furthest satellite Saturn would appear of about 3;times the width, and of about 13 times the area, of our Moon .From the 6th its area would be more than 100 times, and fromthe 7th somewhat less than 80 times, that of the Moon . Itwould be seen to pass through phases similar to those observedfrom the rings, except that instead of the one-half (see p. 376),which would in general be seen from them, the whole of theilluminated phase would be visible, a comparatively narrowzone of the planet being all that would be hidden by the ring-system.

An observer upon the satellites would look at the ringsnearly edgewise, and see them as a line of light,* widest in itsmiddle portion where it would be nearest to him, but every-where very narrow. At the times when Saturn ’s disc wouldhe seen in its full phase, the full extent of the line of ringsupon each side would also be visible; at other times only aportion of their circumference corresponding to the extent ofthe planet’s phase, although a faint additional effect might beproduced by any part which might rise above the general levelof the rest. Were it not for the thinness of the rings theirappearance would be very beautiful, as they would, when viewedfrom the innermost satellite, extend about half-way across thewhole width of the heavens, the nearest portion of which, ifthey be supposed to be 100 miles in thickness, would be ofabout ird of the apparent width of the Moon .

It would not be profitable, nor can we afford the requisitespace, to discuss the eclipses of the Sun by these satellites, as

* The outermost satellite, owing to the greater tilt of its orbit to thatof Saturn , might occasionally see a little more of the flat surface of therings.