[AZ-Observing] Re: Comparison of M78 LRGB Vs Hydrogen Alpha
- From: "Jon Christensen" <jonc97@xxxxxxx>
- To: <az-observing@xxxxxxxxxxxxx>
- Date: Sat, 14 Jan 2006 13:44:14 -0700
Hi Joe,
The feature you mention is to me one of the striking things about this
comparison.
Here is my uninformed and haphazard wild guess:
M78 is a fairly large reflection nebula, part of which is obscured in the
foreground by gas and dust that emits in Ha wavelengths. We see the blue
reflection nebula through holes in this partially obscuring emission nebula.
That one spot you speak of is a hole through the emission nebula that allows
the blue reflection nebula behind it to shine through, yet is dark in the
Halpha photograph because it does not shine at that wavelength.
Anybody who knows the real story feel free to sent me straight. :-)
Jon Christensen
----- Original Message -----
From: "Joe Larkin" <joeclarkin@xxxxxxxxx>
>I like how that gray nebula in the middle is just black in the Ha
>picture.
>
>Does this mean it is a foreground reflection nebula that looks like a
>dark nebula since it is knocked way down by the Ha filter? Or is it
>an emission nebula that doesn't emit at all in Ha?
>
>Or a combination of dust and gas that doesn't emit in Ha AND obscures
>the stuff behind it when imaged at Ha?
>
>Joe Larkin
>
--- Jon Christensen <jonc97@xxxxxxx> wrote:
> I posted this to the SBIG list a while back but I thought it would
> be of interest to you folks.
> Peter Erdman shot a photo of M78 and vicinity in Hydrogen Alpha and
> noted how completely different it looked than my LRGB version.
> Hydrogen Alpha filters filter out all but a narrow band of light at
> about 656 nm which is in the red spectrum and is associated with
> glowing hydrogen. LRGB pictures are made by using clear, red,
> green and blue filters to try to approximate what the human eye
> could see if it could accumulate light as efficiently as a CCD
> camera. I made a mouseover comparison of both images:
>
> http://members.cox.net/jonc95/M78compare/m78.htm
>
>
>
> The Hydrogen Alpha filter filters out much of the blue reflection
> nebulosity of the main nebula, and brings out interesting swirly
> patterns in the gas not visible in the LRGB version. A lot of
> people mix LRGB and Hydrogen alpha photos to try to get the best of
> both in their pictures, but some think what you lose in the process
> is not worth it.
>
> Jon Christensen
> --
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