Now that we got Jupiter up and running, it’s time to bring Saturn into the picture. Jupiter reached opposition last month when it passed closest to the Earth for the year. It’s still incredibly bright and will remain a beacon in the southern sky throughout summer and into early fall. But now the focus shifts to the ringed planet which comes to opposition tomorrow, July 9.
On that date, Earth will slide directly between Saturn and the sun, and the two planets will be closest. As always, close is a relative term in astronomy. Saturn lies 840 million miles (1.4 billion km) away. While lacking the eye-blasting power of Jupiter, the largest planet, Saturn still attracts attention. It shines at magnitude 0 (equal to Vega) low in the southeastern sky three fists to the lower left of Jupiter at nightfall from the constellation Sagittarius the Archer. We know it better as the Teapot.
You’ll find the planet tucked toward the eastern side of the Teapot just under another asterism called the Spoon. What goes better than a spoonful of sweetener with your cup of tea? Sagittarius has one more asterism dubbed the Milk Dipper. Stars in the teapot’s handle and top are repurposed as a dipper. And the milk? That’s the nearby Milky Way, of course. Saturn will take you to all three of these delightful stellar patterns.
In 10x binoculars the planet looks slightly out of round, caused by its rings, which blend with the ball of the planet to make an oval shape. Don’t feel too bad if you can’t see the rings this way — Galileo couldn’t either. A small telescope magnifying 30-50x will reveal what appears to be a single ring around Saturn’s globe, while a modest 6-inch telescope will show three. The outermost and narrowest is the A ring, the second one in is wide and bright and called — you guessed it — the B ring. A narrow, dark gap, Cassini’s Division, separates the A from B rings. It’s only 3,000 miles (4,800 km) wide and looks like a delicate black thread. Very beautiful!
The innermost or C ring is translucent and sometimes tricky to see. Look for it as gray shading in front of the planet where Saturn’s globe “touches” the rings. Depending on the quality of your sky. Try a magnification of at least 150x to see it clearly.
All the rings are composed mostly of highly-reflective water ice compared to Saturn’s globe which is decked with dense clouds made of ammonia ice with traces of hydrocarbons that tint it the color of butterscotch. You can really see the difference in a telescope when you compare the two. Telescope users will also notice that the rings are especially bright right now due to the opposition surge or Seeliger Effect.
When our backs are to the sun, as it is when we view a planet at opposition, objects in front of us are squarely lit by sunshine streaming over our shoulders. Any shadows cast by icy fragments in Saturn’s rings are hidden directly behind them. Without shadows to ‘darken’ the scene, the rings appear briefly brighter. Compare the view now and again in several weeks to see if you can spot the difference.
The rings are still tipped close to their maximum, making 2019 the best time for many years to see all three bright rings along with Cassini’s Division. Oh, and don’t forget the moons. We can only see four of Jupiter’s moons in a typical telescope, but Saturn offers up five in a 6-inch scope and eight in larger amateur instruments. Titan looks like a little “star” and hangs near the planet every night of the year like a dog on a lease, circles Saturn every 16 days.
Iapetus is so far out it takes 79 days to complete an orbit. When it’s west of Saturn, it appears bright because its ice-covered hemisphere is turned toward the Earth. When east of Saturn, it’s quite a bit fainter because we see the dark side, which is coated in dark, organic compounds. Lucky for us, Iapetus is currently west of Saturn and brightest at magnitude 10. Go for it now through early August.
The moons Rhea, Dione and Tethys are visible in a 6 to 8-inch telescope and cluster close the planet, unfortunately in the glare of the rings. Enceladus, the moon that spurts salt-water geysers, is closer in yet and dimmer Mimas closest. I’ve yet to see that last one. Hyperion is very faint at 14th magnitude but distances itself far enough from the planet that it’s within range of a 10 to 12-inch scope under dark skies.
You can keep track of the Saturn’s five brightest moons at Sky & Telescope’s interactive Saturn’s Moons site. Or download Stellarium, pick a date and time and zoom in on Saturn. That’s what I do. Then I screen-grab the map, send it to my e-mail and call it up on my phone when I’m at the telescope.
Right now, we see the north face of the rings and northern hemisphere of the planet. Through my 10-inch scope I can make out a half-dozen moons on a typical nights and spy the gray north equatorial belt (yes, Saturn has belts like Jupiter only they’re fainter and more closely spaced) and the gray cap of cloud over the north polar region. When the air is very steady look for the shadow of Saturn’s globe cast on the ring plane with a magnification of 150x or higher. Right now, that shadow’s directly behind the ball, but later this summer it will be easier to spot when it swings off to the west.
How’s this for fun? On the evening of July 15, the Full Buck Moon will park directly under Saturn. They’ll only be about a degree apart with closest approach of ¾° around 3 a.m. on the 16th. What a wonderful bonus. Clear skies!