Observers in the Midwest can catch Callisto passing near the planet’s northern limb.
Callisto just skims the northern edge of Jupiter on May 11, not long before Io begins a transit and Ganymede, hidden in the planet’s shadow, reappears to the northeast. Europa lies to the west, beyond this field of view. Credit: Astronomy: Roen Kelly
The gas giant Jupiter still dominates the constellation Taurus as it sets in the west after sunset. Jupiter now stands just to the right of Alheka (Zeta Tauri), one of the tips of the Bull’s two horns. The magnitude –1.9 planet remains the brightest point of light in the constellation, making it easy to center in your telescope tonight.
While three of Jupiter’s four Galilean moons frequently pass in front of or behind Jupiter, the larger orbit of Callisto and the tilt of the gas giant’s equator relative to Earth mean that this moon often “misses” the planet from our point of view, passing far north or south of its poles.
Tonight, though, Callisto just grazes Jupiter’s northern limb from about 9 P.M. to 9:30 P.M. CDT as it passes from west to east. The moon is most directly north of the planet’s pole at about 9:20 P.M. CDT. Note that this event is best seen in the Central time zone of the U.S. — Jupiter is setting for East Coast observers at this time, while the sky is still quite light in the Mountain time zone, as it’s shortly after sunset in this region.
However, even those farther west will still get a bit of a show, as Io begins a transit from east to west across the disk of Jupiter at 9:07 P.M. MDT. Just a few minutes later, have your gaze locked on the region just off Jupiter’s northeastern limb, as Ganymede will suddenly pop into view, having crossed from west to east through Jupiter’s long, dark shadow.
The planet’s fourth Galilean moon, Europa, lies far west of the planet all night tonight.
Sunrise: 5:48 A.M.
Sunset: 8:05 P.M.
Moonrise: 7:32 P.M.
Moonset: 4:56 A.M.
Moon Phase: Waxing gibbous (99%)
*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.
