The inset at the upper left shows the 1/2 degree angular size of the full moon for scale. So Lovejoy’s coma appears only a little smaller (but much fainter) than a full moon on the sky, and its tail is visible for over 4 degrees across the frame. …
Blown by the solar wind, the comet’s tenuous, structured ion tail streams away from the Sun, growing as this Comet Lovejoy heads toward perihelion, its closest approach to the Sun, on Jan. 30.
While diatomic carbon (C2) gas fluorescing in sunlight produces the coma’s green color, the fainter bluish tail is tinted by emission from ionized carbon monoxide (CO+).
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