Astronomy Magazine highlights Tethys transit visible Oct 17‑18 2026 for amateur observers

On October 17, 2026, you can watch Saturn’s moon Tethys transit (when a moon passes in front of Saturn’s disk) beginning around 9:35 P.M. EDT, best seen from the eastern United States.

You can look to the southeast around 9 P.M. local daylight time to find Saturn, the brightest object in that part of the sky, located in the constellation Cetus. At the observing location (40° N 90° W), sunrise is 7:14 A.M., sunset is 6:16 P.M., and moonrise is 2:35 P.M. local time.

Through any telescope, you can see Saturn’s disk, its broad rings, and its brightest moon Titan far to the east. The three next‑brightest moons visible are 10th‑magnitude Tethys, Dione, and Rhea.

Before the transit, you will see Tethys approach Saturn’s northeastern limb (the edge of Saturn’s disk) while Rhea lies southeast and Dione southwest of the planet. During the transit, Tethys becomes difficult to see because its small disk contrasts poorly with Saturn’s bright cloud tops.

You will see Tethys’ shadow (the dark silhouette it casts on Saturn) follow the moon, appearing just northeast of it around 9:50 P.M. EDT. Tethys clears Saturn’s northwestern limb shortly after midnight EDT, ending the transit.

You will see Dione move toward Saturn’s southeastern limb. Dione’s motion brings it closer to Saturn’s edge.

Dione will be occulted by Saturn shortly before 12:45 A.M. EDT on the 19th, visible only in the Eastern time zone. This occultation hides Dione behind Saturn’s disk.

Only astroimagers using advanced video‑capture techniques can detect Tethys and its shadow during the transit.

Even without watching the transit, you can enjoy Saturn’s rings and its other visible moons. The Moon at 10 P.M. local time from the same site is waxing gibbous (54%) illumination.

Astronomy Magazine’s Sky This Week column notes the Tethys transit as a noteworthy chance for you. After the transit, you can again see Tethys on the western side of Saturn, north of the rings.