Saturn’s two-toned moon reaches its greatest western elongation, when it shines brightest far west of the ringed planet.
Saturn’s moon Iapetus has vastly different albedos (brightnesses) on its two hemispheres. One side is much darker than the other, so as the moon orbits and rotates, it shows different faces to Earth. When it is at western elongation, the brighter face is turned toward us, and the moon shines around magnitude 10. Credit: NASA/JPL-Caltech/Space Science Institute
Saturn’s two-faced moon Iapetus reaches its greatest western elongation today. At western elongation, the moon’s lighter hemisphere is turned toward Earth, making it brightest and easiest to view through a telescope.
First, locate Saturn above the eastern horizon around 4 A.M. local daylight time, roughly 90 minutes before sunrise. At this time, the planet should be high enough (25°) that it’s not too affected by the turbulent air close to the horizon, but the sky should also be dark enough to allow you to pull Iapetus out from the background. Saturn itself shines at magnitude 1.0, hanging beneath the Circlet of Pisces and to the far upper right of blazing Venus, which lies closer to the ground and shines a brighter magnitude –4.3.
Once your telescope is locked on Saturn, you’ll likely notice its biggest and brightest moon, 9th-magnitude Titan, sitting about 3’ east of the ringed planet. Iapetus, one magnitude fainter, lies on the other side of the world, some 8.5’ to Saturn’s west. Several 10th-magnitude moons cluster closer to the rings as well — Dione and Rhea lie just west of the planet, less than about 1’ away. Tethys may be visible to the west of the planet for some East Coast observers as well, but it’s moving into Saturn’s shadow and then behind the planet in an occultation for most U.S. observers.
Sunrise: 5:31 A.M.
Sunset: 8:29 P.M.
Moonrise: 10:17 P.M.
Moonset: 6:09 A.M.
Moon Phase: Waning gibbous (98%)
*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.
