Sky Talk July 2011: Saturn’s Last Harrah

July offers the final opportunity this year to view the magnificent ringed planet Saturn while still well-placed above the southwestern horizon. And thanks to a famous technique using the Big Dipper as a guide to constellation identification, it’s easier than ever to identify! Plus there’s an added bonus: while a telescope is needed to see the planet’s rings themselves, thanks to its proximity to a prominent star there’s also something here for naked-eye and binocular skywatchers as well.

Right after darkness falls on July evenings, golden Saturn graces the southwestern sky as it nears the end of this year’s apparition. The brighter planets are easy to identify not only because of their prominence in the sky but also because they don’t twinkle like stars do. (See the June 2008 installment of Sky Talk.) But right now there’s also a fascinating way to identify the ringed planet even from the heart of a light-polluted city. It uses the well-known phrase “Follow the arc to Arcturus.” This refers to following the curve of the Big Dipper’s handle downward in the sky to the radiant orange star Arcturus in the constellation Bootes. And continuing that arc also brings you to the bright bluish star Spica in Virgo.

In July following this curve more exactly brings you to Saturn, with Spica lying noticeably to its east. Careful scrutiny with the unaided eye will show the 3rd-magnitude star Porrima (or Gamma Virginis) sitting nearly on top of the planet, just to its right. The view in binoculars and low-power telescopes like the Edmund Astroscan will be quite striking with both star and planet in the same field of view less than half a degree apart. Saturn’s slow orbital motion eastward will also be evident from week-to-week by comparing the gap between the two objects.

Looking closely, you’ll notice that Saturn actually appears to be elongated or egg-shaped in appearance seen in steadily-held 7x to 10x binoculars due to the presence of its rings. However, it takes a minimum magnification of about 25x to make out the ring system itself (which typically appears to be all but blended with the planet itself at such low power). With the 35x eyepiece on the Scientifics 60mm refractor the rings are clearly seen encircling the planet and with its 87x eyepiece Saturn looks like some exquisite piece of cosmic jewelry floating in space! The view continues to become ever-more spectacular as telescope size and magnification increase. In large observatory-class instruments, the sight of the ringed planet is beyond description. On public viewing nights at such facilities visitors are often heard shouting out loud with delight at what they are seeing!

Mention should also be made of Saturn’s largest moon Titan. Telescopes show it looking like an 8th-magnitude star changing position from night-to-night as it orbits the planet. This huge satellite (bigger than the planet Mercury, explaining its easy visibility at such a great distance from us) can also be glimpsed in binoculars under good sky conditions.

—James Mullaney
Former assistant editor at Sky & Telescope magazine & author of eight books on stargazing.