We nestle up to one of the universe's most magnificent sights tonight. Once a year, Saturn and Earth line up on the same side of the sun and come closest to one another. Tonight the distance between the two planets reaches its minimum: 830,981,800 miles or 1,337,335,574 km. While hardly a stone's throw, the ringed planet is 189 million miles closer compared to Jan. 23, when it was on the opposite side of the sun.
Being closer means that Saturn will shine bigger and brighter than usual. If you have a telescope, blow off the dust and take it outside for a look at those incredible rings. Like the full moon, Saturn lies opposite the sun in the sky right now, so it rises at sunset in the southeast. Because its path lies at a low slant to the horizon, give the ring king some time to clear the trees first.
From many locations, a good time to start looking is around 10-10:30 p.m. Saturn shines at magnitude 0.2 from Capricornus the Sea-goat and makes a striking, wide pair with brighter Jupiter, located about 20 degrees, or two fists, farther to the left (east).
Although the planet's rings number in the thousands, only three are typically visible in small and medium telescopes: the outer A-ring ; the wide and bright B-ring, and the innermost, translucent C-ring. A narrow, dark gap called Cassini's Division separates Ring A from B. A 4-inch telescope will show the A and B rings (and Cassini gap), but a slightly larger 6-inch scope is required for the faint C-ring.
Small scopes will also reveal the North Equatorial Cloud Belt as a single, dark stripe across Saturn's northern hemisphere. When seeking these features, use the highest magnification your telescope will allow. I say "allow" because turbulence in Earth's atmosphere can limit what you see by making the image blurry.
I like 50x to 75x for my first look at the planet and rings. Then I bump the magnification to around 150x to get in closer. On rare, good nights of steady air, I crank the power up to 250x or more and pretend I'm in orbit.
Saturn takes about 29 years to circle the sun. Like the Earth, its axis is tilted, but at a slightly larger angle of 26.7 degrees. As Saturn plies its orbit, first the north pole is tilted our way. A quarter of an orbit later, we get a sideways view, facing the equator. At the halfway point, the south pole tips toward us, and so on. Our changing perspective also causes the rings, which lie above the planet's equator, to tilt from fully open to edgewise to open again. Right now the rings are inclined 18 degrees with their north face visible. Maximum tilt of 27 degrees occurred a couple years back.
When their inclination is 0 degrees, they can totally disappear from view in smaller scopes. That sounds preposterous until you realize that despite having a diameter of 170,000 miles (270,000 km) the rings are only about 30 feet (9.1 meters) thick!
Saturn's rings are composed primarily of chunks of water ice from roughly 10 feet (3 meters) across down to a half-inch (1 cm). Countless smaller bits and pieces down to a millimeter salt-and-pepper the scene. As it is, ice is a good reflector of light, making the rings appear brighter than the cloud-shrouded, yellowy globe. But for several days around opposition, they’re even more radiant than normal due to the Seeliger Effect. At that time, we view the planet with the sun directly at our back the same way we see a full moon. This viewing angle hides the shadows cast by the ring particles, which makes them brighten up.
Saturn has 82 known moons, more than any other planet. With a small telescope, you can see several of them, including Titan, the brightest at magnitude 8.5, along with Rhea, Dione, Tethys and Iapetus. Anytime you want to know what moons are visible where, use Sky & Telescope's Saturn moon finder. Just key in the time then read their positions from the graphic.
After you've finished up with Saturn, you can explore nearby Jupiter. It comes closest to your front door on Aug. 20, when it reaches opposition. Two bright evening planets with one at opposition — what a wonderful way to start a new month.
"Astro" Bob King is a freelance writer for the Duluth News Tribune. Read more of his work at duluthnewstribune.com/astrobob.