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Post Laureate

Reged: 09/30/08

Loc: S. of Chicago's light dome
Re: Color in Orion new [Re: Starman1]
      #5544106 - 11/28/12 03:36 PM

I see a wide range of colors in M42, and it follows what Don concluded above: It varies. For me, and on the best of nights, I see the following in these scope sizes:

70mm refractor: Hints of blue, mostly gray
90mm refractor: A bit more blue, mostly gray
114mm reflector: Quite a bit of blue, the rest gray
130mm reflector: A lot of blue, some green, the rest gray
150mm reflector: Lots of blue, lots of green, some gray
250mm reflector: Blue, green, some orange, and a hint of dusty rose, the remainder gray

Those are on the best nights, and my eyes only. My kids see more color than me in smaller scopes; my wife sees less. I have asked other people to detail what they see, and it varies by person, quite widely.

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Carpal Tunnel

Reged: 06/07/07

Loc: Saskatoon, SK
Re: Color in Orion new [Re: magic612]
      #5547639 - 11/30/12 06:28 PM

On a night of excellent transparency after observing for several hours I could see hints of dusty pink in M42...and lots of green of course. So yes, I think you saw what you saw and good for you!

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professor emeritus

Reged: 04/13/12

Re: Color in Orion new [Re: Starman1]
      #5547951 - 11/30/12 10:03 PM


There are two issues at play, with M42:
1) lab studies show that when 2 gray squares, illuminated to *barely* the limit of scotopic vision, but one a tiny bit brighter than the other, are presented to the observer, we all see the fainter one as "reddish" or "pinkish" and the brighter one as "greenish". This alone says we should trust our eyes very little when used at or near the limits of vision, if color is seen.
That we all see it is NOT a sign the color is there, merely that all of us have eyes that work the same way.

2) when observing M42 (and heaven knows I've looked at this nebula with 2" to 60" aperture at least a thousand times over the years), sometimes more colors than simply greenish-gray or pinkish-gray present themselves.
It seems that, on those nights, the nebula is SO bright in the telescope that a quick glance away from the scope shows that night vision has been damaged.
And the range of colors seen extends to yellowish-beige, bluish, pinkish, purplish, reddish, mauves, and simple grays, and nearby NGC1977 appears quite blue. One such night, I drew a simple map of the nebula, indicating where I saw each color, and compared it to a color photograph of the nebula, and found I had correctly indicated where each shade was found. So I am certain that, under the right conditions, colors can be seen in the Orion nebula. My vision at the time was probably mesopic, and not purely scotopic.

3) But these colors are not ALWAYS visible. As an experiment, I tried viewing the nebula through an H-alpha filter. Only the brighter sections could be seen, and the brightest part, even in H-a, was the central region.
When using a filter that transmits H-b and O-III, the entire nebula can be seen. That's not surprising since every nebula that emits H-a also emits H-b at a lower level, and because our peak sensitivity at night hovers around 500nm (near the H-b wavelength).

4) Recently, I've had a chance to compare narrowband filters that have substantial transmission at H-alpha with those that have zero transmission shorter than 700nm.
It may very well be that the restriction of bandwidth creates a greater ability to see the reddish colors than a non-filtered view, because the non-filtered view didn't present them as strongly. Or that the diminishment in brightness of the entire field resulted in that red/green illusion at the limit. How to tell?
It appears the reds I am used to seeing must be real, because they are visible in the filters WITH H-a transmission, but disappear with the filters that do not have H-a transmission.

5) Different observers have different sensitivities to colors, but it seems that on the nights where I see many colors, or very strong colors, so does everyone else in the observing site, and with a wide variety of apertures. I did not record particulars about the observations, but a memory search recalls that these were nights of exceptional transparency (very low extinction) and darkness.

So what can you say about the visibility of colors in M42/M43/NGC1977?
--it varies from person to person
--it varies from night to night
--it varies according to the filter used
--it varies by aperture (the reds were stronger in larger aperture)
--if "at the limit", the colors may not be real.

But if you have a night where you can see ANY tint to the fainter interior of the nebula, looks at those sections on either side of the central region and see if one side appears yellower than the other. If you see that, I believe you are seeing REAL colors in the nebula. Just don't expect to see them all the time.

Awesome...well informed and written post.

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