October 2011

Today’s Astronomy Picture of the Day is a spectacular view of four of the moons of Saturn and a partial view of the rings. Image and the explanation below courtesy of APOD and NASA. You may need to click on the image to enlarge it to original size to see the fourth moon “Pan.”

Explanation: A fourth moon is visible on the above image if you look hard enough. First — and farthest in the background — is Titan, the largest moon of Saturn and one of the larger moons in the Solar System. The dark feature across the top of this perpetually cloudy world is the north polar hood. The next most obvious moon is bright Dione, visible in the foreground, complete with craters and long ice cliffs. Jutting in from the left are several of Saturn’s expansive rings, including Saturn’s A ring featuring the dark Encke Gap. On the far right, just outside the rings, is Pandora, a moon only 80-kilometers across that helps shepherd Saturn’s F ring. The fourth moon? If you look closely in the Encke Gap you’ll find a speck that is actually Pan. Although one of Saturn’s smallest moons at 35-kilometers across, Pan is massive enough to help keep the Encke gap relatively free of ring particles.