Page:Astronomy for Everybody.djvu/241
planet is at B, the ring is presented to the sun edgewise. After passing B the sun shines on the south (lower) side at an inclination which continually increases till the planet makes C, when the inclination is at its greatest,
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Fig. 40.—Showing how the Direction of the Plane of Saturn's Rings remains Unchanged as the Planet moves round the Sun.
twenty-seven degrees. Then it diminishes as the planet passes to D, at which point the edge of the ring is again presented to the sun. From this point to A and B the sun again shines on the north side.
The earth is so near the sun in comparison with Saturn that the rings appear to us nearly as they would to an observer on the sun. There is a period of fifteen years, during which we see the north side of the ring, and at the middle of which we see them at the widest angle. As the years advance, the angle grows narrower and the rings are seen more and more edgewise till they close up into a mere line crossing the planet, or perhaps disappear entirely. Then they open out again, to close up in another fifteen years. A disappearance occurred in 1892 and another will take place in 1907.