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#1 stray1

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Posted 01 December 2013 - 02:47 AM

Weird question. I've been doing a little research on our sun and have learned that it can take upwards of 100,000 years for a light photon emitted by the core to travel through the radiation zone and outward to where we can see it here on earth.

Does the sun also absorb photons emitted or reflected from outside sources (e.g.,from planets or moons, or from distant stars) and add them back into the mix?

:grin:

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#2 brianb11213

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Posted 01 December 2013 - 04:30 AM

Weird question. I've been doing a little research on our sun and have learned that it can take upwards of 100,000 years for a light photon emitted by the core to travel through the radiation zone and outward to where we can see it here on earth.

Does the sun also absorb photons emitted or reflected from outside sources (e.g.,from planets or moons, or from distant stars) and add them back into the mix?

Short answer, yes, but the incoming radiation is such a small proportion of that arriving at the solar photosphere (visible surface) that the effect is totally imperceptible. This is not the case in some binary systems where a large, cool star is warmed one one side by a very close, hot companion, with noticeable effects on the light curve as the system rotates about its common centre of mass. (But even here the effect is merely surface heating. The core of the larger star is unaffected.)

Another point: the photons generated by nuclear fusion reactions in the solar core do not actually take tens or hundreds of thousands of years to reach the surface. They bump into atoms along the way, are absorbed and later the energy is released when (a) new photon (or photons) is (or are) emitted, travelling in different directions. This happens very many times in a "drunkard's walk" before the energy finally arrives at the solar surface (photosphere) and is (more or less) free to travel outwards where it might be detected somewhere in the universe at large. It's just as well that the original photons get absorbed as, at the high temperatures present in the solar core, they are very damaging but invisible X & gamma rays.

#3 SkipW

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Posted 01 December 2013 - 12:30 PM

Does the sun also absorb photons emitted or reflected from outside sources (e.g.,from planets or moons, or from distant stars) and add them back into the mix?

:grin:

-stray-

Great question! :waytogo: The answer is yes, indeed.

Believe it or not, the sun behaves very nearly like an ideal black body - something that absorbs all electromagnetic radiation that falls on it, regardless of wavelength, and emits electromagnetic radiation in a continuous spectrum that depends only on its temperature.

http://en.wikipedia....wiki/Black_body

The sun's temperature is pretty much determined by the nuclear reaction in its core, but incident starlight, cosmic rays, cosmic microwave background radiation, radio waves, etc., and reflected sunlight, although probably way too small to be significant, are absorbed and do add in.

Edit: Grammar

#4 stray1

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Posted 02 December 2013 - 02:00 AM

Thanks for the info!

:grin:

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#5 RussL

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Posted 02 December 2013 - 10:18 AM

What happens to photons once they hit our retina?

#6 brianb11213

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Posted 02 December 2013 - 10:53 AM

What happens to photons once they hit our retina?

The energy is absorbed. What happens is that some of the energy is used to break a bond in special molecules (rhodopsin) present in the retinal cells & this generates a nerve signal which travels to the brain. The rest of the energy just makes the retina very slightly warmer, the heat is carried away by the bloodstream. The rhodopsin is regenerated by ongoing metabolic activity in the retinal cells.

#7 RussL

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Posted 02 December 2013 - 11:40 AM

What happens to photons once they hit our retina?

The energy is absorbed. What happens is that some of the energy is used to break a bond in special molecules (rhodopsin) present in the retinal cells & this generates a nerve signal which travels to the brain. The rest of the energy just makes the retina very slightly warmer, the heat is carried away by the bloodstream. The rhodopsin is regenerated by ongoing metabolic activity in the retinal cells.


Thanks. I've always wondered. Amazing to think that a photon travels all those distances to end in my retina.






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