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As my calendar states it is March 17th, St-Pat's Day, I was wondering
if there's anything green up in the skies that we could observe to
mark the day?

Rol

Stars, because they are effectively backbody radiators,would be shades of
pink yellow and blue, but never green. Thats becaue if a body is hot enough to emit at 500nm
(green) it will also be emitting lots at 600nm (red) which would make it yellow.
To glow green they'd have to be out of thermal equilibrium.


A cold body could be green too, buy reflectance spectrum. Hmm. The onely green
cold stuff I rememver seeing is probably the blue-green festoons on Jupiter.

That leaves emission nebulae. They can glow at individual spectral lines (a very
non-thermal process) and there are tons of then that emit at the OIII line.

But you'd need a really bright one to percieve as green. So I think observing
M42 with a 16 inch or larger aperture is the best bet.

How anyowe know any chartreuse objects to observe?

-a d