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Saturn’s moons are on the move: Dione skims behind the ringed world in an occultation as brighter Titan stands nearby.
Titan is easy to spot near Saturn on August 21. Additionally, at 5 A.M. EDT, the 10th-magnitude moon Dione is preparing to just skim over the northern pole of the ringed planet. Observers in the western two-thirds of the U.S. will have the best views, as the sky will begin to grow light along the East Coast as Dione crosses north of Saturn. Only moons brighter than mid-10th magnitude are shown here. Credit: Stellarium/Oleg Pluton
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August 20: Dark, flat Plato
Turn your gaze southeast early this morning to find Saturn already some 30° high, shining so brightly it’s easy to pick out among the dim stars populating this region. You’ll want a telescope — even a small one will do — to view the planet’s lovely ring system, which stretches some 43” from end to end. That’s more than twice the planet’s apparent diameter, which is currently 19”. The rings are showing off their southern side, and the southern pole of Saturn is visible as well.
Now look just northeast of the planet — you should be able to identify Titan, Saturn’s largest moon, glowing at mid-8th magnitude less than an arcminute away. If you come back tomorrow morning, this moon will have slid westward in its orbit, standing northwest of Saturn the morning of the 22nd. It takes about 16 days in total for Titan to complete a full orbit.
If you have dark skies and a larger scope, you may also spot 10th-magnitude Rhea, Dione, and Tethys near Saturn as well. Around 2 A.M. EDT, all three are east of the planet, with Dione to the northeast (but closer in than Titan), Tethys to the east, and Rhea to the southeast. Over the next few hours, you can watch Dione moving west at a much faster pace than Titan — observers in the Central time zone and areas west of this will see Dione skim just north of Saturn’s pole around 5 A.M. CDT.
Sunrise: 6:17 A.M.
Sunset: 7:48 P.M.
Moonrise: 3:52 P.M.
Moonset: —
Moon Phase: Waxing gibbous (69%)
*Times for sunrise, sunset, moonrise, and moonset are given in local time from 40° N 90° W. The Moon’s illumination is given at 10 P.M. local time from the same location.
Alison Klesman is senior editor of Astronomy magazine. She holds a Ph.D. in astronomy and has studied a variety of topics, from minor planets to supermassive black holes.