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Why is the Flame Nebula in Orion's Belt orange (not red)

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#1 airscottdenning

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Posted 29 March 2019 - 11:51 PM

The Flame Nebula near Alnitak is a distinct orange-gold color, not even close to the same deep red of hydrogen alpha emission of the nearby IC 434. 

 

Is this dramatic difference in color due to a different emission spectrum and gas composition? Or is it colored by intervening dust? Or what?

 

 



#2 aa6ww

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Posted 30 March 2019 - 12:14 AM

Its only been shades of gray when Ive seen it.

 

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#3 Juicy6

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Posted 30 March 2019 - 03:10 AM

Maybe light from nearby blue giant Alnitak combined with own red Ha light gives orange?

 

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#4 Araguaia

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Posted 30 March 2019 - 06:39 AM

I see the Flame as a rich amber color, and IC 434 as the faintest dark red in the sky.  Nearby NGC 2023 is paler than the Flame, more like off-white, although it is difficult to make out the hue with its central star washing it out.

 

I love looking at that region of the sky at low power precisely because of the juxtaposed hues on the different nebulas.



#5 bobzeq25

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Posted 30 March 2019 - 09:23 AM

The Flame Nebula near Alnitak is a distinct orange-gold color, not even close to the same deep red of hydrogen alpha emission of the nearby IC 434. 

 

Is this dramatic difference in color due to a different emission spectrum and gas composition? Or is it colored by intervening dust? Or what?

IC434 is a pretty pure Ha emitting source.  The Flame combines Ha with reflection from dust.  I can't think of another way to get orange, what would be the emission line, and how on Earth <grin>  would it be strong enough?

 

The color thing becomes really interesting with imaging.  Assume the camera passes Ha well, ie no unmodded DSLRs.  LRGB images still tend to overemphasize the reflection component of the Flame.  Sometimes people make the Flame white, and (I think inevitably) portray IC434 as orange.  I don't think that's correct, although it has some charm.

 

You can see a wide range of interpretations in this thread.  Or on astrobin or with Google images.

 

https://www.cloudyni...rsehead-nebula/

 

What I admire is people who capture varying shades of color in the Flame.  Using HaRGB, I couldn't do that, it's a pretty uniform orange.

 

https://www.astrobin...4117/G/?nc=user

 

A great example of how the colors we portray are simply various interpretations of the data.


Edited by bobzeq25, 30 March 2019 - 09:27 AM.


#6 GlennLeDrew

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Posted 21 April 2019 - 02:24 AM

My theory. The Flame is a highly excited nebula, in the mode of M42. Such nebulae have additional blue-green emission from oxygen. This makes for a more pink-magenta hue in many images, compared to deeper red for such less-excited specimens as IC 434. But in the case of the Flame there is considerable reddening by intervening dust, which de-bluing tends toward an orange-red hue.

 

There are loads of other examples all over the sky. If one has either the long-extinct Desktop Universe software, or the newer Starry Night Pro Plus (which uses the same all-sky photo mosaic), a visual scan will differentiate the pinkish, less-obscured nebulae from the more orange-ish, notably attenuated nebulae. Again, for the more highly excited examples; the more "pure red", low surface brightness and low-excitation nebulae exhibit far subtler color shift with reddening.

 

I mentioned DTU and SNPP software mainly because of the very uniform treatment of the images in putting together the final mosaic, which makes possible a sky-wide nebula color comparison. Other carefully treated, *visual* emphasis color surveys/mosaics should serve similarly.


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#7 David Knisely

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Posted 24 April 2019 - 01:15 AM

There may also be just a little H-Beta emission in the Flame, so that, coupled with nebular scattered light and dust in the nebula, might shift the color just a hair to more of an orangish hue.  I do recall in my 14 inch one night using my 14mm ES100 eyepiece (135x, 44.7' arc TFOV) and my Lumicon H-Beta filter being able to just see both the Horsehead and much of the Flame at the same time in the field.  Clear skies to you.




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