Re: Time Machine revised?

On 5 May 2007 10:51:01 -0700, Girish <girishbhat6620@xxxxxxxxx> wrote:
On May 5, 11:53 am, David Librik <lib...@xxxxxxxxx> wrote:
I always had the impression it was common knowledge in the 1890s.

Well, I AM an ignorant layman but I always had the vague impression
that understanding that the sun will end up as a red giant pre-
supposed understanding the thermo-nuclear reactions taking place in
the sun.

Actually? It's a hypothesis you can construct from the Hertzsprung-Russell
diagram (basically a 2-D plot of the stars we can see, using color and
true luminosity as the axes) plus hypotheses about how old the various
segments of the galaxy where you can see different types of stars are. We
get a cross-section snapshot at this moment in time, effectively, but it
contains stars at all ages (or so we assume, because otherwise we'd be
really Weird for some unknown reason), so we can thread them together into
a life story, much like arranging a series of photos into temporal order.

And this doesn't require knowing thing one about what's going on inside
said stars. The diagram was first made around 1910, thirty years before
the innards' cycles started being understood, and still "represented a huge
leap forward in understanding stellar evolution" (wikipedia). But that is,
yes, 15 years after The Time Machine, she was wrote. At that point we knew
there _were_ red giants, I believe, but not really how the lifecycle of
an average star might go.

Dave
--
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It's not the clock that slows the hour The definition's plain for anyone to see
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.

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