Mercury’s greatest western elongation December 2025: All you need to know

Mercury will reach its greatest western elongation—its maximum angular distance from the sun—on December 7, 2025. At that time, the planet will be 20.7°W from the sun. This will be the best time to observe Mercury in the morning sky.

Mercury’s greatest western elongation in December 2025

Moment of greatest elongation: Mercury will reach its greatest western elongation on December 7, 2025, at 21:00 UTC (4:00 p.m. EST).

When to see: Mercury will be visible in the morning sky from late November to late December 2025.

Thereafter, Mercury will rapidly approach the sunrise glare as it moves toward its superior conjunction behind the sun on January 21, 2026.

Where to look: Look above the eastern horizon shortly before sunrise. Mercury will appear above Venus in late November 2025.

Visibility throughout the globe: Mercury’s greatest western elongation in December 2025 will favor observers in the Northern Hemisphere.

In the Northern Hemisphere, Mercury will appear higher in the sky before sunrise because of the steeper angle of the ecliptic, making the planet easier to observe.

In the Southern Hemisphere, Mercury will appear very low in the sky before sunrise and will be difficult to observe in the bright morning twilight.

Visibility through a telescope: Mercury will appear 61% illuminated (nearly in its first quarter phase) and 6.7 arcseconds in diameter at its greatest western elongation.

Thereafter, Mercury will appear thicker and smaller each day until it reaches its superior conjunction.

Brightness of Mercury: After emerging in the morning sky in late November, Mercury’s brightness will rapidly increase until it reaches its superior conjunction (i.e., its full phase) on January 21, 2026, when the illuminated side of the planet (i.e., the day side) completely faces us.

What does “Mercury at greatest western elongation” mean?

Elongation means the angular distance from the sun. Mercury at western elongation means it is west of the sun in our sky, so it rises before sunrise and sets before sunset.

Mercury at greatest western elongation means it is farthest west from the sun in our sky, so it rises as early before sunrise as possible. This marks the best time to see the planet in the morning sky.

Around its greatest western elongation, which occurs once every 3 to 4 months, Mercury is visible in the morning sky for only 2 to 3 weeks.

Mercury’s greatest western elongation in 2025-2026

Here are the dates of Mercury’s greatest western elongation in 2025-2026:

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