Comet Lovejoy's Tail
From NASA’s Astronomy Picture of the Day
Sweeping
north in planet Earth's sky, Comet Lovejoy's greenish coma and blue
tinted ion tail stretched across this field of stars in the
constellation Taurus on January 13.
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.
That corresponds to
over 5 million kilometers at the comet's estimated distance of 75 million
kilometers from Earth.
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
January 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+).
