Catching 2026 Jovian Moon Mutual Eclipse Season

• The 2026 Jovian moon mutual eclipse season is expected to occur between late 2026 and early 2027, when Jupiter’s major moons will perform a mutual transit-eclipse event. This season is part of a bidecadal cycle, occurring approximately every five years. The event is characterized by the moons passing each other in front of one another as seen from Earth. Callisto will cast a shadow on Jupiter from May 20th, 2025, until August 5th, 2028. The middle of the season occurs around mid-October 2026.

• The moons’ orbits are slightly tilted relative to Jupiter’s equatorial plane, with the tilt of the moons from Io to Callisto being less than a degree. Jupiter itself is tilted just over a degree relative to the ecliptic plane. The innermost three moons, Ganymede, Europa, and Io, are in a 1-2-4 resonance, meaning Io completes two orbits for Europa’s one. This resonance allows for rare triple shadow transits, such as the 2015 event and the next one in 2032.

• Observing these events is challenging due to the small size of the moons. The largest moon, Ganymede, is only 1.3 inches in diameter. Even small telescopes can capture a moon in total eclipse behind another, as it fades from view and returns. The eclipses and occultations can be complex, with different types of events like total, annular, and partial eclipses. The season is a unique opportunity for observers to witness the complex interplay of Jupiter’s moons.

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