Looking for a sky event this week? Check out our full Sky This Week column.
December 26: The Moon shares the sky with Saturn
Io and its shadow cross Jupiter overnight tonight with only 20 minutes between them. Finding Jupiter is likely familiar by now, as the gas giant shines brightly in Gemini near the heads of the Twins. For most of the evening, there are three moons east of Jupiter’s disk: Io is closest, then Europa, with Ganymede farthest out. Callisto is alone west of the planet.
Io approaches the eastern limb as the hours pass, and its shadow appears first on the cloud tops at 12:28 A.M. EST (early on the 28th in EST only, late on the 27th in all time zones farther west). Io follows 20 minutes later, at 12:48 A.M. EST. The pair lies centrally on the disk around 1:45 A.M. EST, now the 28th in the Eastern and Central time zones.
The shadow maintains its lead and slips off the western limb of Jupiter around 2:45 A.M. EST on the 28th, with Io following by 3:05 A.M. EST. After that, there are two moons on either side of Jupiter, now that Io lies to the west with Callisto.
Sunrise: 7:21 A.M.
Sunset: 4:42 P.M.
Moonrise: 11:38 A.M.
Moonset: —
Moon Phase: Waxing gibbous (54%)
*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.
