Thursday, June 15, 2017

SATURN AT OPPOSITION AND THE SEELIGER EFFECT Taken by Tom Harradine on June 15, 2017 @ Brisbane, Asutralia

A lucky break between clouds in Brisbane tonight allowed me to capture the planet Saturn at opposition. This evening Saturn, Earth, and the Sun formed a straight line with Earth being in the middle. Our view of Saturn at this time means that the planet is being lit by the Sun from directly behind us.

Compare these two images of Saturn at opposition tonight (right) and Saturn a month ago (left). Apart from some differences in image quality (tonights view was through less steady atmosphere and thus more blurry) there are two noticeable differences.

Firstly, note that the shadow of the planet, visible on the rings at the top right of the left image, has disappeared at opposition. It will reappear in a few days on the other side. Also, note that Saturns icy rings are more brightly lit at opposition compared to beforehand. This is due to what astronomers call the Seeliger Effect.

This effect describes the surging of brightness at opposition due to the backscattering and retroreflecting (think catseyes) of light from small particles in the rings and the disappearance of shadows which makes each ring particle appear full (think mini full Moons) and thus more bright.

Saturns rings will go back to their normal brightness over the next few days as it starts rising in the east soon before sunset.

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