270. _General Appearance of the Rings._--Saturn is surrounded by a thin flat ring lying in the plane of its equator. This ring is probably less than a hundred miles thick. The part of it nearest Saturn reflects little sunlight to us; so that it has a dusky appearance, and is not easily seen, although it is not quite so dark as the sky seen between it and the planet. The outer edge of this dusky portion of the ring is at a distance from Saturn of between two and three times the earth's diameter. Outside of this dusky part of the ring is a much brighter portion, and outside of this another, which is somewhat fainter, but still so much brighter than the dusky part as to be easily seen. The width of the brighter parts of the ring is over three times the earth's diameter. To distinguish the parts, the outer one is called ring _A_, the middle one ring _B_, and the dusky one ring _C_. Between _A_ and _B_ is an apparently open space, nearly two thousand miles wide, which looks like a black line on the ring. Other divisions in the ring have been noticed at times; but this is the only one always seen with good telescopes at times when either side of the ring is in view from the earth. The general telescopic appearance of the ring is shown in Fig. 291. [Illustration: Fig. 291.] [Illustration: Fig. 292.] Fig. 292 shows the divisions of the rings as they were seen by Bond. 271. _Phases of Saturn's Ring._--The ring is inclined to the plane of the planet's orbit by an angle of twenty-seven degrees. The general aspect from the earth is nearly the same as from the sun. As the planet revolves around the sun, the axis and plane of the ring keep the same direction in space, just as the axis of the earth and the plane of the equator do. When the planet is in one part of its orbit, we see the upper or northern side of the ring at an inclination of twenty-seven degrees, the greatest angle at which the ring can ever be seen. This phase of the ring is shown in Fig. 293. [Illustration: Fig. 293.] When the planet has moved through a quarter of a revolution, the edge of the ring is turned towards the sun and the earth; and, owing to its extreme thinness, it is visible only in the most powerful telescopes as a fine line of light, stretching out on each side of the planet. This phase of the ring is shown in Fig. 294. [Illustration: Fig. 294.] All the satellites, except Japetus, revolve very nearly in the plane of the ring: consequently, when the edge of the ring is turned towards the earth, the satellites seem to swing from one side of the planet to the other in a straight line, running along the thin edge of the ring like beads on a string. This phase affords the best opportunity of seeing the inner satellites, Mimas and Enceladus, which at other times are obscured by the brilliancy of the ring. [Illustration: Fig. 295.] Fig. 295 shows a phase of the ring intermediate between the last two.