[Vision2020] Human Activity Accelerating Astronomical Effects By Factor Of 10 Million

[Ted Moffett]

Paul et. al.

Wonderful accessible (no incredible math required!) educational short course
in stellar evolution at this web site, from "down under:"

http://www.physics.usyd.edu.au/~helenj/Galaxies/SG3.pdf

Ted Moffett

On 4/23/07, Paul Rumelhart <godshatter at yahoo.com> wrote:

> Ted,
>
> As it happens, I've just started learning about stellar evolution and main
> sequence stars for a project I am working on at home.  Here's a quick
> rundown of what I've found out so far (it's complicated - I still have a lot
> to learn):
>
> As I understand it in general terms, the Sun is in the hydrogen-fusion
> portion of it's life which is called the "main sequence".  Stars spend most
> of their lives in this stage in a general equilibrium.  The fusion from the
> core is in effect pushing back against the gravity of all that hydrogen and
> other atoms.  The hydrogen is being fused into helium at the core, thus the
> makeup of the stellar core is changing.  This will continue more-or-less at
> an equilibrium (compared to other stars and other phases of development) for
> about 10 - 12 billion years.  The Sun is thought to be about 5 billion years
> old at the moment.  The age at which a star uses up it's hydrogen fuel is
> based mostly on it's mass.  At some point in the future, the hydrogen that
> is hot enough to fuse in the core will start to run out, and the core will
> have built up a large amount of hot helium "ash" that is too cold to fuse
> (helium requires a much higher temperature to start fusion).  Thus, the
> force pushing against the gravity of the rest of the Sun will be less and
> the Sun will contract a bit which will raise the temperature and ignite some
> of the hydrogen closer to the core.  This will cause the Sun to expand a bit
> after the hydrogen shell around the inner helium core has started fusion.
> This is a "last gasp" before the fuel in the core runs out.  Once the
> hydrogen in the core is gone, there is no force pushing back against the
> weight of the outer layers of the star and the core collapses.  The pressure
> internally skyrockets and gets quickly hot enough to ignite some more of the
> layers surrounding the core.  Since there is more fuel in a larger volume
> surrounding the core, it expands in luminosity and thus radius.  Even though
> the luminosity is increasing, the temperature at the surface will decrease
> because the radius is increasing which is why the star turns red.  It takes
> millions of years to get through this phase, and then the hydrogen runs out,
> the star collapses, and the temperature gets high enough to ignite the
> helium at the core.  The helium will burn out too, and then some other
> element (carbon?) will ignite, etc.
>
> The spike that the article was talking about before the red giant stage
> must be the "last gasp" I talked about above.  I wasn't aware that there
> would be a gradual increase in luminosity to that stage, but maybe there is
> one.
>
> However, it's my understanding that the forces in the Sun, while
> understood at a generic level of abstraction, are still quite chaotic and
> unstable.  Since the Sun is the major impactor on temperature here on Earth
> (the second major impact being the internal heat from the Earth's core), any
> small change in the Sun's output could have drastic effects on us since we
> are extremely fragile.  The Sun is hot enough to keep us warm from a
> distance of about 11 light-minutes.  I also understand that the outer layer
> of the Sun is much, much hotter than the core.  The core is at about 5700K,
> the outer surface is at about 10 million K.  Why the outer surface is so
> much hotter is still an unsolved problem in astrophysics.  This lack of
> understanding frightens me.  Solar outputs varies by about 0.04% on an
> eleven year cycle, and solar flares can vary output by 5%.  How stable is
> this phase of stellar evolution, really?  We've been around for a mere few
> million years, only the last few thousand of which we've had the ability to
> write things down.  This is a small fraction of time for the Sun.  Our
> observations of the Sun has occurred over such a small timescale that we can
> basically say that we've only seen it as a static observation.
>
> I think the 0.8 billion year number you quoted is the time it will take
> for the slow process of hydrogen fusion at the core to raise the Earth's
> temperature 5%.  This seems to imply that the solar output will increase
> slowly from now up until that value is reached.  This is at odds with other
> things I have read, which state that the Sun will cool as the hydrogen in
> the core starts to run out before it increases again right before becoming a
> red giant.  When the Sun expands to be a red giant, it will happen in a few
> million years and go from twice it's output to some much larger number
> (which I haven't found, yet) that will be enough to boil off the seas and
> the atmosphere both.  However, the variability of the Sun at this stage may
> affect us more than the slow increase or decreases in temperature that we
> will see in this current phase.
>
> I am not, however, making the claim that humans aren't impacting the Earth
> by a large amount.  Nor am I making any other claims having to do with
> global warming.  I am just letting you know what I have so far assimilated,
> much of which may (and probably will be) found out to be wrong.  I am not
> staking out a position here, and will not feel obligated to defend any of
> what I have said in the future.  I'm not an expert, and expect to continue
> to learn and unlearn things as we go.
>
> Paul
>
>
> Ted Moffett wrote:
>
>
> All-
>
> Our sun will eventually cause fatal increases in Earth temperature in its
> inevitable evolution into a red giant star.  When will these temperature
> impacts become significant?  The article below estimates that in 800 million
> years the sun's impact will raise Earth temperatures by 5 degrees, the same
> amount predicted by some global warming models for the human impact on
> global temperatures in the next century:
>
> http://www.sussex.ac.uk/press_office/media/media191.pdf
>
>
> http://72.14.253.104/search?q=cache:hAqjwfgBKT4J:www.sussex.ac.uk/press_office/media/media191.pdf+time+remaining+Earth+biosphere+sun+expansion&hl=en&ct=clnk&cd=6&gl=us
>
>
> "As a first application, let us ask how long it will take for the
> temperature of the Earth to rise by 5 degrees (the rise anticipated in the
> next century or so if the current human-induced greenhouse effect continues
> unchecked).  The equation predicts it will take the evolving sun about about
> 0.8 billion years to produce this rise- so human activity may
> be accelerating astronomical effects by a factor of about 10 million."
> ------
> This puts the highly doubtful claim that the current warming trend on
> Earth is mostly due to increases in solar activity into perspective, it
> seems.
>
> Ted Moffett
>
>
>
> ------------------------------
>
> =======================================================
>  List services made available by First Step Internet,
>  serving the communities of the Palouse since 1994.
>                http://www.fsr.net
>           mailto:Vision2020 at moscow.com <Vision2020 at moscow.com>
> =======================================================
>
>
>
>
> =======================================================
>  List services made available by First Step Internet,
>  serving the communities of the Palouse since 1994.
>               http://www.fsr.net
>          mailto:Vision2020 at moscow.com
> =======================================================
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://mailman.fsr.com/pipermail/vision2020/attachments/20070424/e489420e/attachment.html