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... The brightest red was in the Huygenian region, but the color did extend to some degree away from that area.

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and here is a quote from another post of yours #2005477

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... the parts of M42 which show reddish colors to me tend to be well *away* from central Huygenian region and the Trapezium rather than adjacent to them

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From these descriptions I understand that the parts that really stimulates the cones (first quotation) are not the same that show reddish color (the second quotation). I mean that I understand that "some degree away" il less away that "well *away*".
So, are you meaning the same regions? And which exactly are these regions?

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These are two COMPLETELY DIFFERENT OBSERVATIONS! One was with a red filter, and the other was with a different filter like the NPB or the dual passband OIII. You are comparing apples and oranges. With a red filter, *all* the visible nebulosity was red: PERIOD.

With the dual passband filter, the red was primarily not in the inner Huygenian region but in the area around it and in spots well away from the Huygenian region, like patches in the "wings" of the nebula or the area south of the inner Huygenian region. The inner Huygenian region appears a greenish-blue color in the NPB filter. In the H-beta filter (which also has a red passband), the Huygenian region appears more bluish but the area around it appears more reddish than in the NPB filter, as the H-Beta contribution is weaker than the H-alpha line.

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David W. Knisely
Hyde Memorial Observatory
http://www.hydeobservatory.info

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