Saturn's Moons

Every fifteen years, thanks to the nuances of Earth’s and Saturn’s orbits, Saturn’s rings appear edge-on to our line of sight. During a “ring plane crossing” these incredibly thin ornaments virtually disappear in all but the largest telescopes.

We might bemoan the loss of Saturn’s rings (they are a major draw at public star parties), but without the glare they produce, we can better view Saturn’s retinue of moons. 8th magnitude Titan is the easiest and can be glimpsed in a common 60mm refractor. Rhea (magnitude 9.5), Tethys (10.0) and Dione (10.2) will require 4 to 6 inch scopes. An adventurous skygazer, using a telescope in this size range, might try for magnitude 11.5 Enceladus

Now that Saturn is past opposition and well-placed in the evening sky, take the opportunity to view and identify some of those moons you’re never before seen. A moderately high magnification will increase contrast and make the fainter moons more readily visible. Carefully sketch the field, then go inside to confirm your “kills.” If you’re fortunate enough to own a copy of the RASC Observer’s Handbook 2009, turn to pages 245-248 for a graphic showing the positions of Saturn’s major moons at any date and time of the year. You can also use Sky and Telescope’s interactive Saturn moon finder. Go to www.skyandtelescope.com, scroll down to “Interactive Observing Tools,” click on “Saturn’s Moons,” then submit the date and time of your observation. You’ll need to register to obtain this service, but it’s free. Take advantage of the current Saturn ring-plane crossing. We won’t experience another until 2025! Your comments on this column are welcome. E-mail me at gchaple@hotmail.com.