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Saturn at Opposition

March 21, 2010

Today is the first full day of spring here in the northern hemisphere. Sunlight is returning to the north pole after six months of darkness, as the pole begins to dip sunward.

The same thing happened about a year ago on a planet that's putting on a good show this month. Saturn lines up opposite the Sun, so it rises at sunset and remains in view all night. It's at its brightest, too -- the golden planet outshines all but a handful of other planets and stars.

Like Earth, Saturn is tilted on its axis, and at about the same angle. So as Saturn orbits the Sun, it appears to "nod" up and down as seen from the Sun. The north pole nods toward the Sun for half of its orbit, with the south pole nodding sunward the other half.

And just as on Earth, that creates seasons, with changes in weather. When the Cassini spacecraft arrived at Saturn almost six years ago, it was winter in the northern hemisphere. A blue "haze" encircled the planet at high northern latitudes, in the zone where sunlight faded to darkness.

As the northern winter ended and spring began, though, the haze disappeared, replaced by the planet's customary shades of yellow and tan.

One big difference between the seasons on Earth and Saturn is their length. It takes 30 years for Saturn to complete a circle around the Sun, so each season lasts more than seven Earth years. So each of Saturn's poles has a 15-year season under the Sun -- and a 15-year season of darkness.

Script by Damond Benningfield, Copyright 2010

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