Rings of Neptune
The rings around Neptune could not be seen from Earth with strong telescopes. The evidence that they were there was first seen when scientists were watching the planet as it passed between the Earth and a star. (When this happens, the light of the star is blocked. This is called "stellar occulation".) Scientists watched this happen 50 times, and on five of those times in the early 1980s they saw the star give a little "blink" just before or after the planet covered it. This meant that rings around the planet were blocking the light, but the rings were not complete.