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Energy transport in the Sun



 
 
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  #1  
Old August 1st 04, 07:24 PM
Martin Frey
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Default Energy transport in the Sun

1982, Robert Noyes, The Sun Our Star says

The energy released in (the core) as a gamma ray ... is destined to
spend the next 10 million years struggling to the surface.

BUT 2002, Freedman and Kauffmann, Universe, says

As a result, it takes approximately 170,000 years for energy created
at the sun's centre to travel 696,000 km to the solar surface and
finally escape as sunlight.

Any thoughts on why this has idea changed so radically in 20 years?
(Or if either or neither is right?)

--
Martin Frey
http://www.hadastro.org.uk
N 51 02 E 0 47
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  #2  
Old August 1st 04, 11:07 PM
Andrew Urquhart
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*Martin Frey* wrote:
1982, Robert Noyes, The Sun Our Star says

The energy released in (the core) as a gamma ray ... is destined to
spend the next 10 million years struggling to the surface.

BUT 2002, Freedman and Kauffmann, Universe, says

As a result, it takes approximately 170,000 years for energy created
at the sun's centre to travel 696,000 km to the solar surface and
finally escape as sunlight.

Any thoughts on why this has idea changed so radically in 20 years?
(Or if either or neither is right?)


In lectures a few years ago I believe I was told it was of the order of
1 million years. Alas I don't recall much else of those particular
lectures now. However, speculating wildly and trying to remember how
photon random walks drift[1], the only thing I can think of is if the
first figure is a calculation based solely on the small net outward
motion in a photon's 'random' walk, and the second figure is this random
walk drift plus effects due to deep convection and that it's this
convective effect that has been modelled and added in the last 20 years.

[1] I'm trying to remember if random walk drift is due to the pressure
gradient, therefore the density gradient, and the effect this has on the
'mean time before collision'. So a photon is able to travel ever so
slightly further in the direction away from the core before it collides
with a particle because there's ever so slightly less material in that
direction than in the core-ward direction.
--
Andrew Urquhart
- Contact me: http://andrewu.co.uk/contact/
- Apologies for the wrong timestamp on my post - blame my ISP
- 'Staccato signals of constant information
A loose affiliation of millionaires and billionaires' - Paul Simon


  #3  
Old August 1st 04, 11:57 PM
Martin Frey
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Posts: n/a
Default

"Andrew Urquhart" wrote:

In lectures a few years ago I believe I was told it was of the order of
1 million years. Alas I don't recall much else of those particular
lectures now. However, speculating wildly and trying to remember how
photon random walks drift[1], the only thing I can think of is if the
first figure is a calculation based solely on the small net outward
motion in a photon's 'random' walk, and the second figure is this random
walk drift plus effects due to deep convection and that it's this
convective effect that has been modelled and added in the last 20 years.

[1] I'm trying to remember if random walk drift is due to the pressure
gradient, therefore the density gradient, and the effect this has on the
'mean time before collision'. So a photon is able to travel ever so
slightly further in the direction away from the core before it collides
with a particle because there's ever so slightly less material in that
direction than in the core-ward direction.


Thanks, Andrew

That's my understanding - from the books - of how the net outward flow
is achieved. I know there's been some refinement of the depth of the
convection zone thanks to solar seismology but not enough to cope with
a 60 fold reduction from 10 million years or even a 6 fold reduction
from your remembrance of 1 million.

Maybe my 1982 book just got it wrong (shame because its a very
readable acount that I had rated highly).

--
Martin Frey
http://www.hadastro.org.uk
N 51 02 E 0 47
 




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