269. _The Satellites of Saturn._--Saturn is accompanied by eight moons. Seven of these are shown in Fig. 287. The names of these satellites, in the order of their distances from the planet, are given in the accompanying table:-- Number. Name. Distance Sidereal Discoverer. from Period. Planet 1 Mimas 120,800 0 22 37 0.94 Herschel 2 Enceladus 155,000 1 8 53 1.37 Herschel 3 Tethys 191,900 1 21 18 1.88 Cassini 4 Dione 245,800 2 17 41 2.73 Cassini 5 Rhea 343,400 4 12 25 4.51 Cassini 6 Titan 796,100 15 22 41 15.94 Huyghens 7 Hyperion 963,300 21 7 7 21.29 Bond 8 Japetus 2,313,800 79 7 53 79.33 Cassini The apparent brightness or visibility of these satellites follows the order of their discovery. The smallest telescope will show Titan, and one of very moderate size will show Japetus in the western part of its orbit. An instrument of four or five inches aperture will show Rhea, and perhaps Tethys and Dione; while seven or eight inches are required for Enceladus, even at its greatest elongation from the planet. Mimas can rarely be seen except at its greatest elongation, and then only with an aperture of twelve inches or more. Hyperion can be detected only with the most powerful telescopes, on account of its faintness and the difficulty of distinguishing it from minute stars. _Japetus_, the outermost satellite, is remarkable for the fact, that while, in one part of its orbit, it is the brightest of the satellites except Titan, in the opposite part it is almost as faint as Hyperion, and can be seen only in large telescopes. When west of the planet, it is bright; when east of it, faint. This peculiarity has been accounted for by supposing that the satellite, like our moon, always presents the same face to the planet, and that one side of it is white and the other intensely black; but it is doubtful whether any known substance is so black as one side of the satellite must be to account for such extraordinary changes of brilliancy. [Illustration: Fig. 288.] _Titan_, the largest of these satellites, is about the size of the largest satellite of Jupiter. The relative sizes of the satellites are shown in Fig. 288, and their orbits in Fig. 289. [Illustration: Fig. 289.] [Illustration: Fig. 290.] Fig. 290 shows the transit of one of the satellites, and of its shadow, across the disk of the planet. THE RINGS OF SATURN.