Why do the rings of Saturn appear from Earth to vary from being very distinct to being almost invisible over a period of a few years

answer:

The same thing that's happening now: we're experiencing a "ring plane crossing." As Saturn goes around the sun, it periodically turns its rings edge-on to Earth—once every 14-to-15 years. Because the rings are so thin, they can actually disappear when viewed through a small telescope.

Explanation:

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