2025, October 3: Double Shadows on Jupiter and the Moon Near Saturn

October 3, 2025: Europa and Io cast their shadows on Jupiter’s cloud tops during early morning hours, while the bright moon draws closer to Saturn in the evening sky.

Jupiter greets the moon during morning twilight.
Photo Caption – Jupiter greets the moon during morning twilight.

by Jeffrey L. Hunt

Chicago, Illinois: Sunrise, 6:50 a.m. CDT; Sunset, 6:28 p.m. CDT.  Times are calculated by the US Naval Observatory’s MICA computer program. Check local sources for sunrise and sunset times.

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Moons’ Shadows Cross Jupiter

Jupiter's volcanically active moon Io casts its shadow on the planet in this dramatic image from NASA's Juno spacecraft. As with solar eclipses on the Earth, within the dark circle racing across Jupiter's cloud tops one would witness a full solar eclipse as Io passes in front of the Sun. (NASA Photo)
Photo Caption – Jupiter’s volcanically active moon Io casts its shadow on the planet in this dramatic image from NASA’s Juno spacecraft. As with solar eclipses on the Earth, within the dark circle racing across Jupiter’s cloud tops one would witness a full solar eclipse as Io passes in front of the Sun. (NASA Photo)

The Observer’s Handbook, along with other resources, is one of the references used to write the articles that appear here. It provides a daily listing of sky events, along with detailed articles and tables about eclipses, star clusters, and planetary satellites.

The monthly almanac notes that two of Jupiter’s satellites, Europa and Io, simultaneously cast their shadows on the Giant Planet’s cloud tops about every 3.5 days. Some of these double solar eclipses are visible from the Americas.

One event occurs after midnight. In mid-America, both shadows are visible beginning at 1:49 a.m. CDT (October 4) when Jupiter is less than 20° above the east-northeast horizon. The moons and their shadows appear to move toward the planet’s western limb. By 3:10 a.m., both shadows are visible while Io and Europa are silhouetted against the cloud tops.

Jupiter’s four largest moons, known as the Galilean Satellites, are visible through a steadily held binocular. They are easier to see through a spotting scope or telescope with less than 50x magnification. The moons’ shadows require about 100x magnification for visibility.

Look for a similar double-shadow event on Jupiter beginning at 3:45 a.m. CDT (8:45 UTC) on October 11. The planet is visible from most of the Americas.

Tonight’s Highlight

Saturn, Moon, October 3, 2025
Chart Caption – 2025, October 3: The bright gibbous moon is in the southeastern sky after sundown, while Saturn is low in the east-southeast.

Tonight’s highlight is the moon as it approaches Saturn. An hour after sundown, the gibbous moon, 87% illuminated, is over 20° above the southeast horizon. It is 5.2° to the lower left of Deneb Algedi, the tail of Capricornus. In the moonlight, use a binocular to see the star.

Saturn, more than 15° up in the east-southeast, is nearly 30° to the lower right of the lunar orb. Each evening the moon draws closer to the Ringed Wonder. In two evenings, the moon is only 2° to Saturn’s upper left.

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