Observing the Rare Mutual Eclipse Season of Jupiter's Major Moons

• From late 2026 through early 2027, Jupiter enters a rare 'mutual transit-eclipse season' where its major moons pass in front of or cast shadows upon one another.
• These events occur every five years, approximately half of Jupiter’s orbital period around the Sun, due to the slight tilts in the orbital planes of the Jovian moons.

Mechanics of the Mutual Events

• Types of occurrences include occultations (one moon passes in front of another) and eclipses (a moon's shadow crosses the surface of another).
• Similar to Earth-based eclipses, these appear in total, annular, and partial formats.
• The mid-point of the current season is expected in mid-October 2026.

Jovian Moons and Observations

• Orbital Resonance: The inner three moons—Io, Europa, and Ganymede—are locked in a 1-2-4 resonance, occasionally enabling rare triple-shadow transits.
• Callisto: The only Galilean moon that can miss Jupiter, it has been casting shadows since May 2025 and will continue until August 5, 2028.
• Viewing Tips: While the moons are tiny (Ganymede presents a 1.3-arcsecond disk), even small telescopes can reveal these mergers and fades. Predicting tools like Stellarium or resources from ICMME and SETI PDS assist in planning observations.