Saturn's Day 
You'd think that after centuries of observations of Saturn, scientists would have a pretty good handle on the planet's basics -- things like its size, distance, mass, and the length of its day. And for the first three items on that list, you'd be right. The last one, though, has proved elusive -- the length of Saturn's day has been tough to pin down.
In part, that's because Saturn is a ball of gas that's topped by clouds. There are no solid features, like mountain ranges or craters, for scientists to track.
Instead, they've tried to get the length of the day by measuring variations in Saturn's magnetic field -- the same technique used to measure the day on Jupiter. Using this technique, though, different spacecraft have come up with a difference of about seven minutes in Saturn's rotation rate.
Last year, a team used yet another technique. The scientists measured the motions of subtle waves in Saturn's atmosphere. The waves provided new details on Saturn's winds -- and a new estimate for Saturn's day: 10 hours, 34 minutes, and 13 seconds -- several minutes shorter than earlier estimates.
Whatever the precise length of the day is, Saturn's high-speed rotation has some important effects. It squashes the planet so that it's much bigger through the equator than through the poles. And it stretches the clouds in Saturn's atmosphere into bands that go all the way around the giant planet.
More about Saturn tomorrow.
Script by Damond Benningfield, Copyright 2009