Comet C/2025 A6 (Lemmon) was the bright green comet that lit up the sky in October 2025, becoming one of the most memorable and widely photographed comets of the decade. This capture was taken from my home in Newport, Oregon. The image is ultra hi-res and will be clear at 300 dpi on a 24" long side print.
You are licensed to use it for your personal (non-commercial) purposes, whether you want to save it as your background or print a large copy for yourself.
What C/2025 A6 (Lemmon) Was
A "long‑period comet" (one that won't come back in our lifetime) discovered on January 3, 2025 by the Mount Lemmon Survey. It follows a highly elongated retrograde orbit, meaning it came from deep in the Oort Cloud and won’t return for roughly 1,150–1,400 years.
Why It Became So Bright
When first discovered, Lemmon was extremely faint (magnitude ~21.5) and expected to peak around magnitude 10, or barely visible in small telescopes. Instead, it brightened roughly 400× more than predicted, reaching magnitude 3.5 on October 24, 2025, making it naked‑eye visible under dark skies.
Ground-based observers reported brightness as high as magnitude 3.8–5.3 around its peak, confirming it as one of the brightest comets of 2025.
Key 2025 Timeline
Closest approach to Earth: October 21, 2025 at 0.596 AU (≈89 million km).
Peak brightness: October 24–25, 2025 (mag ~3.5–3.8).
Perihelion: November 8, 2025 at 0.529 AU from the Sun.
Visibility window: Excellent from mid‑October through mid‑November for Northern Hemisphere evening observers.
Why It Looked Green
Spectroscopy showed a bright green coma produced by diatomic carbon (C₂) fluorescing under solar UV radiation — a hallmark of active long‑period comets. Dust production increased as it neared the Sun, forming a short but distinct tail.
Newport’s dark skies and low horizons gave exceptional views during its peak:
The comet was bright enough for naked‑eye detection.
Its green coma and short dust tail were easily captured in long exposures.
October’s stable coastal weather often provided clear windows between marine layers.
