Chris L Peterson wrote:

On Mon, 10 Jan 2005 19:43:32 +0200, Ioannis wrote:


If I recall right, for nebulae, red usually indicates Hydrogen emissions
and green OIII(?), like in the ring nebula.

What element is responsible for the blue emissions around the Pleiades
or, say, around rho Ophiuchi?

Thanks much in advance.


Generally when you see blue, you are seeing reflection nebulas, not emission
nebulas. The blue is the reflected light from one or more nearby hot stars.
While the stars are basically white, blue is preferentially scattered by gas and
dust (why is the sky blue...)

You mean something like a sort of "Rayleigh scattering" in the nearby area?

If this is the case, doesn't this necessarily imply the existence of gas
in the vicinity of those stars?

Why then doesn't THIS gas emit radiation at all from being excited by
those stars? Or if it does, perhaps the scattering dominates the emission?

Thanks!

_______________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com


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I. N. G. --- http://users.forthnet.gr/ath/jgal/