Sky and Telescope - May 2012 - (Page 54)

OBSERVING

Exploring the Solar System

The King of the Rings
Saturn’s tilt for 2012 treats us to the best view of its rings in ﬁve years.
While many eyes are focused on brilliant Mars dwindling into the distance in Leo, a bigger showpiece planet beckons one constellation to the east, in Virgo. That’s where you’ll ﬁnd Saturn shining with its otherworldly rings. It’s at opposition and closest to Earth in mid-April, when most readers have this issue. It remains nearly as large for months to come as it climbs conveniently higher in the early-evening sky. Saturn is just 5° from Spica this season, outshining the blue-white star by just a bit. Look for this eye-catching pair high in the southeast by 10 p.m. in late April, 9 p.m. in early May, and shortly after nightfall thereafter. If you’ve watched Saturn through a telescope in recent years, its most obvious change for 2012 hits you right away: the rings are open again. They’ve appeared nearly edge-on for the last few years, exactly so in 2009. In April 2012 they’re tilted a good 14° from our line of sight, then 13° from May through August. The rings will continue to open until reaching a maximum of 27° in 2017. Like Jupiter, Saturn is a gaseous world showing us its banded cloudtops. But Saturn is both smaller and farther than Jupiter, and, being colder, its markings are
SOUTH C ring on globe Cassini Division Encke Division RINGS C B

more deeply veiled under high-altitude haze. Even so, my 6-inch scope almost always shows some of Saturn’s banding: the bright Equatorial Zone, the slightly darker North Equatorial Belt (the South Equatorial Belt is behind the rings now), and the dusky North Polar Region. During the 2010–11 apparition, the big event for planetary observers was the outbreak of Saturn’s now-famous Great White Spot (GWS). The whitish band trailing from this huge storm encircled the globe (see page 20). Now the storm has subsided. NASA’s Cassini probe orbiting Saturn no longer detects radio emissions from intense lightning in the storm, but the aftereﬀect of the disturbance can still be seen as a weak whitish band encircling the planet at about 45° north latitude. In the eyepiece, the band appears detectably brighter than its surroundings. High-resolution images reveal slight kinks and knots. Large scopes sometimes show additional tiny white spots: smaller round or oval storms, usually in Saturn’s mid-latitudes. To predict when a spot will return to the same location on the disk from night to night, remember that Saturn’s mid-latitudes rotate once in about 10 hours 38 minutes. Near the equator the planet’s visible layer rotates more rapidly, in about 10 hours 14 minutes. Another noteworthy occurrence in 2011 was the frequent appearance of radial spokes in Saturn’s bright, wide B ring (S&T: July 2011, page 50). The spokes are almost always beyond visual reach but can sometimes be extracted from images. For months these dusky markings appeared and faded with a regularity that might be connected to magnetic eﬀects involving the GWS. So far this year, spokes have been absent.

Things to Look For
Equatorial Zone North Equatorial Belt North Tropical Zone North Temperate Belt Di Direc Direction of rot rotation NORTH Storm remnant North Polar Region

This ﬁrst-rate amateur image comes from Bob English in Kentucky. He took it on February 7th, when Saturn was well up in the early-morning sky, using a 20-inch Newtonian reﬂector and a Point Grey Research Flea3 video camera. Note the faint remnant of the northern hemisphere Great White Spot.

The smallest astronomical telescope should reveal the rings easily and the dark Cassini Division between the A and B rings with a little more eﬀort. The dusky C ring is more of a challenge to spot where it appears against the dark-sky background, but its dark shading is easier to see where it crosses Saturn’s bright face just inside the B ring. The C ring in front of Saturn’s face is often indistinguishable from the rings’ dark shadow at the same latitude — but not this year. The rings cast no visible shadow on the globe for most of April from Earth’s viewpoint, then cast their shadow increasingly poleward above the rings for the next few months.

54 May 2012 sky & telescope

Table of Contents for the Digital Edition of Sky and Telescope - May 2012

Sky and Telescope - May 2012
Table of Contents
Spectrum
Letters
75, 50 & 25 Years Ago
News Notes
Saturn’s Raging Superstorm
Stars Above, Earth Below: Astronomy in National Parks
The Remarkable Case of Comet Lovejoy
In This Section
May’s Sky at a Glance
Binocular Highlight
Planetary Almanac
Northern Hemisphere’s Sky
Sun, Moon, and Planets
Celestial Calendar
Exploring the Solar System
Deep-Sky Wonders
Going Deep
S&T Test Report
New Product Showcase
Telescope Workshop
Planetary Imaging with Your DSLR Camera
Gallery
Focal Point

Sky and Telescope - May 2012