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amcgilly
Post  Post subject: Relationship between starlight and liquid water  |  Posted: Tue Nov 22, 2016 7:05 am

Joined: Tue Nov 22, 2016 6:14 am
Posts: 2

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Hi everyone. I just joined tonight and this is my first post. I have a question for the astrophysicists and chemists out there but this being my first post I'm not allowed to include any links (anti-spam measure) which I need to include to properly post my question. Maybe I'll be allowed in my second post.

Adrian McGilly
Oakland, CA


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amcgilly
Post  Post subject: Re: Relationship between starlight and liquid water  |  Posted: Tue Nov 22, 2016 7:06 am

Joined: Tue Nov 22, 2016 6:14 am
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I have a question for the astrophysicists and chemists out there.

If you look at a graph showing how well water absorbs different electromagnetic waves of different frequencies you will see a very sharp valley in the graph for the range of frequencies we call visible light. See this page for a graph showing this:

http://hyperphysics.phy-astr.gsu.edu/hbase/Chemical/watabs.html

The reason for this gap is that as you move across the spectrum from high-frequency to low-frequency waves, the waves interract in different ways with the water molecules. Some cause vibration, some cause rotation, some have a photoelectric effect, etc. and as a result of that interraction their energy gets absorbed by the water. But visible light's frequencies fall "between the cracks", and don't interract with the water molecules much at all and pass through the water far better than all other frequencies.

This explains why water appears transparent to our eyes, and why we have organs called eyes that detect visible light. As organisms evolved in the ocean, those that could detect what we call visible light had an advantage over those who couldn't, so those 'visible light detectors' got better and better until they became what we now call eyes. This is an 'anthropic' explanation which holds water (sorry for the pun).

But now if you look at the spectrum of EM waves emitted by the sun, you'll see that the strongest waves (i.e. those with the greatest flux) are the ones in the visible range. This is also the case for many stars provided they are in a certain temperature range. There's a chart showing this on this page:

http://www.windows2universe.org/sun/spectrum/multispectral_sun_overview.html

I find that to be an interesting and surprising correlation: the highest-intensity EM waves coming from the sun are precisely the ones that travel the furthest through liquid water.

Aside from anthropic explanations, can anyone offer any scientific/physical/chemical explanation for this correlation?

Thanks in advance for your help.

Adrian McGilly
Oakland, CA


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marnixR
Post  Post subject: Re: Relationship between starlight and liquid water  |  Posted: Tue Nov 22, 2016 11:10 am
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Joined: Thu Aug 04, 2011 8:35 pm
Posts: 4755
Location: Cardiff, Wales

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is this a coincidence that just applies to G-type stars ? or is it applicable to other types ?

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Lynx_Fox
Post  Post subject: Re: Relationship between starlight and liquid water  |  Posted: Fri Nov 25, 2016 8:13 pm

Joined: Wed Dec 30, 2015 5:17 am
Posts: 198
Location: US Pacific NorthWest

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I think the the linked water absorbtion chart is for all phases of water, not just liquid.

Not all stars have peak emissions in the visible, the coolest peak in the IR (e.g. Proxima Centauri M class dwarf) and probably the most numerous, while hottest emit in the UV range.


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