Animation on Saturn's rings Seeliger Effect
Every 378 days, as Saturn approach the opposition, the rings suddenly increase their brightness, outshining the planet's globe before dimming back to their normal appearance.
This brightness surge is known as the Seeliger effect, which is a combination of two physical processes: shadow hiding and coherent backscattering. As the Sun shines from exactly the same direction from which we are observing, the millions of icicle composing the rings are hiding their shadows from view, reaching 100% illumination. Furthermore, reflections off the many irregular bits of rock and dust combine to produce a more intense (coherent) light reflected back. This is similar to highway retro-reflectors shining our headlights back at us at night.
The Seeliger effect is subtle but enough to increase Saturn total apparent brightness by about half a magnitude. This variation is quite evident when images taken at different times around the opposition are mounted in sequence, as I did in this animated PNG, using images I took about 40 days before the opposition, about ten days before the opposition and just close to opposition with the maximum brightening.
Also clearly visible the slightly change of the rings tilting as well as the globe's shadows as the relative position between Earth and Saturn changed among the images.
NOTE: the animation requires modern browser to be seen properly (Chrome/Firefox/Edge..).
