Mercury at Greatest Elongation East — October 2026

Planetary events include oppositions, greatest elongations, and conjunctions — all are geometric configurations that make planets particularly well-placed for observation. At opposition, a planet is directly opposite the Sun in the sky, meaning it is closest to Earth, fully illuminated, and visible all night. Greatest elongation marks when Mercury or Venus appears farthest from the Sun in our sky, making them easiest to observe.

Oppposition occurs for superior planets (Mars and beyond) when Earth passes between the planet and the Sun. The planet rises at sunset and sets at sunrise, remaining visible throughout the night. For inferior planets (Mercury and Venus), greatest elongation east means the planet is visible in the evening sky after sunset, while greatest elongation west means it is visible in the morning sky before sunrise. The angular distance from the Sun determines how easy the planet is to spot.

Opposition dates shift each year because Earth and the outer planets orbit at different speeds. Saturn reaches opposition roughly every 378 days, Jupiter every 399 days, and Mars every 780 days. Mercury's greatest elongations occur roughly every 116 days, alternating between morning and evening visibility. These events are predictable with high precision and are calculated decades in advance.