This Sunday the King of the Rings comes to opposition when it will be closest to Earth and bigger and brighter than at any other time this year. You’ll find the Saturn in the company of Virgo’s brightest star Spica low in the southeastern sky at nightfall.
Opposition literally means “opposite the sun”, and that’s exactly where you’ll find the planet, rising in the east as the sun sets in the west. On April 28 it will be out all night, finally departing at the western horizon at sunrise.
Spica and Saturn will get your attention around 10 o’clock in late April and by early evening in May. Located in the dim constellation of Libra the Scales, Saturn’s a little more than a fist held at arm’s length to the left or east of Spica and nearly a full magnitude brighter. You’ll easily see the difference.
A fair share of the planet’s light comes from it rings. They’re made of chunks of reflective water ice ranging in size from a fraction of an inch up to tens of feet. Since the rings are tipped open at a good angle in 2013 (18-19 degrees), Saturn is brighter now than it’s been in many years.
Saturn’s juxtaposition with Spica presents a nice opportunity to see one of the differences between a planet and star. On nights when the atmosphere overhead is buffeted by winds and eddies, Spica will appear to twinkle as its light is yanked this way and that by turbulence. Saturn, which has a substantial size compared to a point-like star, is much less affected by the airy tumult and usually appears tranquil and steady.
One of life’s greatest small pleasures is seeing the ringed planet through a telescope. Nothing can compare. Most people say it looks fake – that’s because it’s one of the few things in the sky that looks like its photograph. In 10x and higher power binoculars you can tell Saturn’s not round like Jupiter. Because we see the rings tipped partway toward us, they stick out from either side of the planet, giving it an oval shape.To see them distinctly and separate from the ball of the planet requires only a small telescope magnifying 40x or higher.
Unlike the speedier inner solar system planets, Saturn takes 29.5 years to make one cycle around the sun and spends 2-3 years in each zodiac constellation. Because Saturn’s axis is tipped much like Earth’s, we see alternate faces of the ring during its orbit. For the next dozen years, we’ll be looking at the north side. Come 2025, the rings will be edgewise to Earth and appear thin as a thread before they open up again and reveal their south face starting in 2026. An entire cycle takes - you guessed it – 29.5 years.
This coming month the rings are tipped invitingly wide at 18 degrees; maximum tilt of 27 degrees happens in 2017. As you increase magnification in your telescope, you’ll see that the one big ring divides into two or three concentric rings.
Even a small scope will show the dark gap called Cassini’s Division separating the thinner A ring from the wide, bright B ring. If you use a 6-inch or larger telescope, you can pick out the dusky C ring interior the A-B pair. Use 100x and up and look for a grey shading where it crosses the edge of Saturn’s globe. Further divisions in the rings require at least an 8-inch scope and preferably a 12-inch.
Ah, then there are Saturn’s wonderful family of moons. Titan, the biggest and brightest, is a snap to see in any telescope. Even a 6-inch will reveal its orange color caused by chemical smog in the moon’s atmosphere. Rhea, Iapetus, Dione and Tethys can be captured in a 6-inch telescope as well, but Enceladus will probably require 8-incher, since it’s so close to the planet and difficult to pick out from the rings’ glare.
You can also watch for the Seelinger Effect, which happens for several nights around Saturn’s opposition. The ring particles are very effective at reflecting sunlight back to the observer when the sun is shining directly at them (called “backscattering”). This causes the rings to brighten noticeably compared to the ball of the planet.
Check it out and see for yourself. Speaking of the planet, Saturn has cloud belts like Jupiter though they’re much more subtle. The belts of the southern hemisphere are hidden by the rings, but the last time I checked, I could easily see the planet’s dark North Equatorial Belt about halfway between the ring plane and north pole.
Watch for any unusual white patches to develop – Saturn occasionally has storms that bring up fresh material from below the cloud desk. High winds over 1,000 mph can spread the clouds into white spot big enough to see in even a small telescope. A huge storm two and a half years ago grew large enough to chase its tail and encircle the entire planet!