Uranus transit in front of a bright star: the flux of the star is interrupted by the arrival of the planet and is modified during the passage through the atmosphere of the planet at the ingress and egress.
The rings of Uranus were discovered accidentally when observing a star occultation by the planet.
The recorded flux of the star was not consistent with what was expected.
The model of planet using to predict the flux coming from the star had to be replaced by a model explaining the interruption of the signal on both side of the planet: the existence of a ring invisible from Earth was discovered.