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Saturn’s largest moon, Titan, transits with its shadow early this morning, passing over the planet’s northern polar region.

Titan’s shadow sits halfway through its transit at 3 A.M. EDT on September 4. Titan has yet to begin its partial transit. Note that several even fainter moons lie near Saturn’s rings to the east, but they are not shown here because they are likely too faint to spot. Credit: Stellarium/Oleg Pluton

  • Titan’s shadow transit across Saturn begins at 1 A.M. EDT, with the moon itself beginning a partial transit across Saturn’s northern polar region around 5 A.M. EDT.
  • Titan’s shadow transit lasts approximately two hours, concluding by 5:15 A.M. EDT, while Titan’s transit ends fifteen minutes later.
  • A transit of the tenth-magnitude moon Tethys across Saturn is also predicted, occurring between approximately 4:30 A.M. EDT and 6:25 A.M. CDT.
  • Visual observation of Tethys may be challenging, and its shadow is expected to be indistinguishable.

We’re focused on Saturn early this morning to catch a transit of Titan together with its shadow across the ringed world. 

The shadow transits first, beginning at 1 A.M. EDT (note this is early on the 4th in the eastern half of the U.S. but late on the 3rd in the Mountain and Pacific time zones). At this time, Saturn is high in the southeast in the eastern U.S., while appreciably lower and in the east on the West Coast. 

Watch through a telescope as Titan’s shadow slowly appears at the northeastern limb of the planet, taking some 25 minutes to fully emerge. Titan is still far from the limb as it casts its shadow at this time, as Saturn is still more than two weeks from opposition. The moon’s shadow takes about two hours to reach midway across the disk (around 3 A.M. EDT), as Titan slowly closes in. Titan finally begins its transit, which will carry it only partially across Saturn’s northern polar region, around 5 A.M. EDT — not long after the shadow has begun its half-hour-long disappearing act over at the northwestern limb. Titan’s shadow is fully gone from the disk by 5:15 A.M. EDT, and Titan’s partial transit ends 15 minutes later. 

Tenth-magnitude Tethys is also transiting this morning, crossing Saturn between about 4:30 A.M. EDT and 6:25 A.M. CDT (note the time change, as sunrise occurs on the East Coast during the transit). Planetary imagers might be able to pick up the small moon, while it may be invisible to visual observers. Its shadow will likely be indistinguishable as well. 

Sunrise: 6:31 A.M.
Sunset: 7:26 P.M.
Moonrise: 6:03 P.M.
Moonset: 2:40 A.M. 
Moon Phase: Waxing gibbous (89%)
*Times for sunrise, sunset, moonrise, and moonset are given in local time from 40° N 90° W. The Moon’s illumination is given at 12 P.M. local time from the same location.

For a look ahead at more upcoming sky events, check out our full Sky This Week column.