Seeliger effect

[astroavani]

The Seeliger effect
Generally, when you look at Saturn through a telescope before or after opposition, the rings look as bright as the planet's globe. For days at the time of the opposition, however, the rings suddenly intensify in apparent brightness, blinding the globe before returning to its normal appearance.

German astronomer Hugo von Seeliger (1849-1924) noticed this change for the first time in 1887. Because of his pioneering research on its cause, which led him to conclude that Saturn's rings were composed of small particles, the effect was named in honor of that scientist.

Two main physical processes lead to the Seeliger effect: shadow hiding and coherent backscattering. When we see Saturn directly illuminated by the Sun (as it is during opposition), the planet's shadow “hides” behind the globe, putting more surface of the ring in view. As a result, the rings appear to lighten. The same angle of direct illumination also causes the shadows of individual particles in the rings to temporarily disappear, improving the result.
The Seeliger effect, which combined the enhancements of shadow hiding and coherent backscatter, makes Saturn's rings appear brighter the closer the planet is to the opposite side of the sun.
The Seeliger effect, which combines the enhancements of shadow hiding and coherent backscatter, makes Saturn's rings appear brighter the closer the planet is to the side opposite the Sun, as in the top image compared to the bottom.
Christopher Go
But that is not all. Observations of the effect of the opposition on the Cassini spacecraft's Saturn rings, in orbit around the planet, reveal that "coherent backscattering" also contributes significantly to the phenomenon. This occurs when sunlight interacts with the collective particles in the planet's rings; the reflections of many irregular pieces of rock and dust combine to produce a single, more coherent (coherent) light. This light spreads back to our eyes and makes the rings appear lighter.

In contrast, and in the days immediately following, we see the combination of these two mechanisms as a temporary increase in the overall illumination of the rings. The only way to fully appreciate the effect visually, however, is to monitor the planet and its rings during the days around that magical moment - weather permitting.
Source: Astronomy; Stephen James O'Meara

[Merlin66]

This effect was well shown in a recent post on IIS.

The animation shows the dramatic increase in ring brightness at opposition.

http://www.iceinspace.com.au/forum/showthread.php?t=184704