Last updated: September 2025

Comet Lemmon (C/2012 F6): The Southern Hemisphere's Green Visitor

Comet Lemmon with its characteristic green hue

An Extraordinary Comet

Comet Lemmon (C/2012 F6) captivated observers in 2012-2013 with its brilliant green color and exceptional visibility in the southern hemisphere. Discovered by the Mount Lemmon Survey in Arizona, it exemplifies the chemical and physical phenomena that define these icy travelers of the solar system.

What Is a Comet?

A comet is an icy celestial body composed of:

Ices (water, CO₂, methane, ammonia)
Silicates (similar to meteorites)
Organic compounds (including diatomic carbon C₂)

When a comet approaches the Sun (within 3-4 AU), the sublimation of ices creates:

A coma (temporary atmosphere around the nucleus)
One or more tails:
- Dust tail (curved, white/yellowish)
- Plasma tail (straight, bluish)

Scientific note: Unlike asteroids, comets often have highly eccentric orbits, bringing them from the outer solar system (Oort Cloud) close to the Sun.

Comet Lemmon (C/2012 F6) Fact Sheet
Characteristic	Value/Details
Official Designation	C/2012 F6 (Lemmon)
Discovery Date	March 23, 2012 (Mount Lemmon Survey, Arizona, USA)
Orbit Type	Hyperbolic (non-periodic)
Perihelion	0.73 AU (March 24, 2013)
Peak Magnitude	~5.5 (January 2013)
Distinctive Color	Green (C₂ emission at 518 nm)
Visibility	Southern Hemisphere (December 2012 - April 2013)
Minimum Distance to Earth	0.98 AU (February 5, 2013)
Discoverer	A.R. Gibbs
Notable Composition	Diatomic carbon (C₂), cyanogen (CN), silicate dust

N.B.:
Comets with hyperbolic orbits like Lemmon likely originate from the Oort Cloud and pass near the Sun only once before leaving the inner solar system permanently.

Why the Green Color?

The emerald hue of Comet Lemmon results from fluorescence:

Solar ultraviolet radiation excites diatomic carbon (C₂) molecules in the coma.
These molecules then emit light at 518 nm (green) when returning to their ground state.
Cyanogen (CN) also contributes to this color (emission at 388 nm, violet).

Key Observation Timeline
Date	Event	Magnitude	Position
March 23, 2012	Discovered by A.R. Gibbs	20.8	-
December 2012	Visible with binoculars	< 10	Southern Hemisphere
January 9, 2013	Peak visibility	5.5	Sagittarius
March 24, 2013	Perihelion passage	~6	0.73 AU from the Sun
April 2013	Gradual disappearance	> 10	-

N.B.:
A magnitude of 5.5 is the naked-eye visibility limit under a perfectly dark sky. In cities, a magnitude of 4 or less is typically required for unaided observation.

How to Observe a Comet Like Lemmon?

Recommended Equipment:

Suitable Observation Equipment
Equipment Type	Features	Possible Observations
Naked Eye	Dark sky (limiting magnitude > 6)	Fuzzy coma (no details)
Binoculars	10×50 or 20×80	Coma and short tail visible
Telescope	≥ 150 mm aperture	Coma details, dust tail
Photography	DSLR + long exposure (20-60 sec)	Extended tails, colors (with processing)

N.B.:
Swan-Band or C₂ filters enhance gaseous structures in photography but reduce overall light by 30 to 50%.

Scientific Significance

Studying comets like Lemmon provides crucial insights into:

Early solar system composition: Comets are "time capsules" containing materials from the planet formation era.
Sublimation processes: Understanding how ices turn into gas under solar radiation.
Interstellar chemistry: Diatomic carbon (C₂) and cyanogen (CN) in Lemmon are key molecules in astrochemistry.