Comet P46/Wirtanen 2018 Perihelion
Why is it cyan-green in colour?
Pretty green. And look at those concentric rings. I can hear you saying, "it must be photoshopped." Well,
as a matter of fact I did use Photoshop. But I've used it very
carefully so as to minimise artifacts and not introduce any artificial
colour shifts. Comets
can contain many molecules. Hydrocarbons are a common
constituent. Methane, CH4 breaks down to smaller molecules.
One of these molecules, diatomic carbon, (C2) exhibits strong line
emissions in the green part of the spectrum. Another ion, C-H, emits
strongly in the cyan-blue part of the spectrum. The position of these
emission lines is marked on the spectrum diagram.
Unfortunately, when taking the image below, I forgot to refocus the
camera when I moved from my previous subject to the comet so it is
Nonetheless, the concentric rings
are not posterization artefacts, the 28 images were manually pixel
registered very carefully all in 16 bit per channel. The jpeg
below is not very compressed to minimize artefacts and you can click here
to see a 10MB 16 bit png uncompressed version of the image in a new
window. The tail is pointing straight away from us and the rings may be
the result of a series of modest outbursts.