From: Amara Graps (amara@amara.com)
Date: Wed Jan 22 2003 - 17:24:23 MST
Dossy:
>On 2003.01.21, Damien Broderick <thespike@earthlink.net> wrote:
> >
> > Excellent point. In fact, I recall that the mean time to
>the surface for a
> > photon from the core is not just thousands of years, but a
>*million* years.
> > [!!]
>
> That's a comforting thought. The Sun could have blinked out
>hundreds of
> thousands of years ago, and we have absolutely no idea? :-)
Here's why...
At the speed of light, it would take 2.3 seconds for a photon from
the center of the Sun to reach the surface.
However, that photon bumps (random walk) through the radiative zone
and its ionized plasma, so if that photon kept the same energy each
time, it would take about 30,000 years. That's the ideal picture,
though, because the photons are absorbed with less energy, many
times, (sometimes reradiated as more than one photon), so it takes
much longer- about a million years. In the convective zone, (30% of
the outer layers), energy transport is efficient, so I suppose this
part goes faster than the radiative zone.
Some very good descriptions of the physics of the Sun:
http://ircamera.as.arizona.edu/astr_250/Lectures/Lecture_12.htm
http://www-ssg.sr.unh.edu/406/Review/rev8.html
http://www.astro.virginia.edu/~emm8x/astr124/lectures/pdf_format/old/Chapter%2015%20The%20Sun.pdf
-- ******************************************************************** Amara Graps, PhD email: amara@amara.com Computational Physics vita: ftp://ftp.amara.com/pub/resume.txt Multiplex Answers URL: http://www.amara.com/ ******************************************************************** "Every exit is an entry somewhere else." --Tom Stoppard
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