What do the colours represent

[johnb]

Hi

I have been taking pretty pic of deep sky objects for a while using a modded cannon 450d, I have never really thought about the content of the image, so what does say blue, red and brown in an image actually represent ?

Regards

John B

[ronin]

Assuming that the image is true colour and not processed to a palete, they should be the emissions from the gas in the nebula.

Qxygen, Hydrogen, possily methane, nitrogen, I think Orion shows CH4 and even alcohol (Ethanol)

Do not know the specifics ones other then hydrogen is the red bit. Ha or Hydrogen Alpha, that is why the filter id removed in Canons to allow more through.

Looks like Green is Oxygen, O III.

[ollypenrice]

Yes, the reds come mainly from ionized hydrogen and the greens from doubly ionized oxygen. Blues are usually produced when bright starlight is scattered by dust (reflection nebulosity) and the browns are likely to be from dust receiving far less light. So the reds and greens are gasses shining with their own light and the blues and browns will be reflection. The exception would be in galaxies where hot young stars too far away to be resolved will produce diffuse blue light in spiral arms whereas the old red stars of elliptical galaxies and the central bulges of spirals will be redder.

Olly

[Stu]

Thanks Olly, a very nice and concise explanation, even I understood that :-)

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