by Chris Peterson » Tue Apr 25, 2017 2:15 pm
videobear wrote:Why is the coma green, but the tail white?
It is common for relatively low activity comets to have a green coma because the gas they are ejecting has a lot of C
2, which glows green when ionized by the Sun's UV radiation. (If the comet becomes very active, the coma gets dustier and the scattered white sunlight dominates, causing the color to be largely lost.)
The ion tail is mostly made up of CO+, which is of a size that preferentially scatters shorter wavelengths, and thus appears blue. There may also be some active emissions, but I think scatter is dominant. Were the activity higher, we'd probably also see a dust tail, which would be white or slightly yellow.
[quote="videobear"]Why is the coma green, but the tail white?[/quote]
It is common for relatively low activity comets to have a green coma because the gas they are ejecting has a lot of C[sub]2[/sub], which glows green when ionized by the Sun's UV radiation. (If the comet becomes very active, the coma gets dustier and the scattered white sunlight dominates, causing the color to be largely lost.)
The ion tail is mostly made up of CO+, which is of a size that preferentially scatters shorter wavelengths, and thus appears blue. There may also be some active emissions, but I think scatter is dominant. Were the activity higher, we'd probably also see a dust tail, which would be white or slightly yellow.