Green Stars cannot Exist but the Universe does contain Green

[glend (Glen)]

I recommend the Cool Worlds Utube video which sets out the astrophysics reasons detailing why there are no green stars visible to us.

Find it here:

https://youtu.be/vXOYbzQ4jDA?si=6D1aLgG5I-KYoRLO

I do not dispute that green stars cannot Exist in the Universe. However, I have many narrowband images taken over many years, which do appear to include significant green emissions. So where does the interstellar green come from? Generally, my green captures come from nebula areas, and likely stem from heavy Oii presence the gas mix, (which tend into the turquoise segment of the visible spectrum.

The Statue of Liberty object area shows tendrils of green light, so to the Tarantula Nebula; and various super nova remants in various locations.
A glance at the histogram of some of these areas definitely shows the presence of light in the green band, yes it is often well below the red and blue, but it it there.
Of course, our intervention in processing, can create some truly garish colour saturation, so that doesn't count in this question.

Now for observational astronomy green light cannot be detected, as the human eye cannot do long exposures, nor detect specific spectra bands; but for you narrowband imagers, let hear what you think on the subject of green spectra rarity?

[Rob_K]

Green light can be detected naked-eye in bright gassy comets. Green comets are common - diatomic carbon emissions.

Cheers -

[Rob_K]

Oops, not naked-eye of course, but visually through a telescope. Losing it!

[glend (Glen)]

Comets are not stars. If you watch the linked video below, it explains why there cannot be green stars (occurring naturally).

[ChrisD (Chris)]

Our suns peak light output is actually in the green spectrum.

It's interesting that plants only evolved photosynthesis using red and blue and do not use any significant energy from the green spectrum, what a waste.

Chris

[glend (Glen)]

Originally Posted by ChrisD

Our suns peak light output is actually in the green spectrum.

It's interesting that plants only evolved photosynthesis using red and blue and do not use any significant energy from the green spectrum, what a waste.

Chris

Many star spectra do indeed contain Green but it simply disappears as it is blended with the vast amount of red and blue. Watch the video below, it explains it all.

[gary]

Originally Posted by glend

I recommend the Cool Worlds Utube video which sets out the astrophysics reasons detailing why there are no green stars visible to us.

Find it here:

https://youtu.be/vXOYbzQ4jDA?si=6D1aLgG5I-KYoRLO

I do not dispute that green stars cannot Exist in the Universe. However, I have many narrowband images taken over many years, which do appear to include significant green emissions. So where does the interstellar green come from?

Hi Glen,

By chance did you ever take a course in quantum mechanics?

Quantum mechanics is a compulsory second year course for Electrical
Engineers and to the best of my knowledge it is possibly the only
discipline that makes practical use of it. But that matters neither
here nor there for this discussion.

I remember the very first pages of the quantum mechanics text we
used (Eisberg and Resnick) was an introduction to "black body radiation"
and the associated Planck's Postulate.

So what the hell is black body radiation? As we all know, when you heat
something up to a sufficiently high temperature, it can start to glow
in a darkened room. Like a horseshoe in a blacksmith's forge. That
light which is emitted is what is referred to as black body radiation
and it is a function of temperature that follows that curve as the professor
explains in the video. So stars are emitting black body radiation and as he
shows in the video, the nature of the curve is that it will never be
narrowband enough to pass light only in the middle visible wavelengths.

Now when you have the green glow of a nebuia (I see both magenta
and green when I look at M42), that is a different kettle of fish.
That gas is being stimulated by ionizing radiation from a nearby star,
typically in the ultraviolet, which causes electrons in the gas to jump
to a higher energy state (there's that quantum mechanics again) and then
fall back and emitting photons.

It's like the difference between an incandescent light bulb and a florescent tube.
The light is generated in two entirely different ways and the physics differs.

I know the professors video was directed at the general public but I
found he was somewhat lax in not explaining that color is not some
attribute of the physical world. Color comes about from processing in
our brain. The universe does not have red, green and blue light but
long, medium and short wavelengths of radiation in what we perceive
as the visible spectrum. Though it is convenient for us to say, "this star
is red" or "this star is blue", that may lead some people to think "color"
is some attribute of the physical world. It is not. Color is in the mind.

[Rob_K]

Originally Posted by glend

Comets are not stars. If you watch the linked video below, it explains why there cannot be green stars (occurring naturally).

Yes of course. My comment was in regard to your statement that "...for observational astronomy green light cannot be detected, as the human eye cannot do long exposures".

Cheers -

[gregbradley]

I often wondered why I would get some mild green gradients in my deep sky images at my dark site which has virtually no light pollution and certainly not any in the imaging zone.

Then when I started doing nightscapes I started seeing greenish tinges or even bright green sky's in some images. It's called air glow. It's either green (most common) or red depending on which chemical is reacting. Red is sodium.

Also light pollution is usually strongest in the green channel.

This would be a factor of seeing green in images.

I have not seen any green in regular LRGB images over countless images now.
If you see it in narrowband that may be because Ha images are usually displayed in the green channel.

A possible explanation.

Greg.

[gary]

Originally Posted by gregbradley

Then when I started doing nightscapes I started seeing greenish tinges or even bright green sky's in some images. It's called air glow. It's either green (most common) or red depending on which chemical is reacting. Red is sodium.

Hi Greg,

The fact that many people could see green tints in M42 when looking
through a telescope was a puzzle up until around 1927.

In fact it could also be detected through spectrographs as bands
around 500nm wavelength - in the part of the visible light spectrum we
perceive as green.

This was such a big mystery that it was speculated that there must be
some unknown new element which was coined "Nebulium".

Then with the coming of quantum mechanics the penny dropped.
It was not a new element at all. It was being created by electrons
in doubly-ionized oxygen (OIII) making transitions.

In order to reproduce it you need a particularly rarified atmosphere
such as in deep space. Or in the high-atmosphere of Earth where
the phenomena will cause the greenish tinge of airglow.

Airglow is the reason why even at the best dark sky locations the sky
is never completely black. When someone says, "I went to such
and such a place and outdoors at night it was so dark that you
could not see your hand in front of your face", I know it must have
been pretty cloudy

Who have become good at modelling airglow is Hollywood. More
specifically the computer animation profession such as the likes of
Pixar. In order to create realistic depictions of the night sky in the
movies, the software includes airglow modelling.

How we as humans perceive and process color is completely different
to how CCD's and digital photography processes color information.
For example, "white balance" in cameras is an engineering kludge
to compensate for the fact the set of transformations the camera performs
on the data is not like how our eye and brain does it but to try and
produce an outcome that looks similar.

[gregbradley]

Thanks for the explanation Gary.

Greg.