On 17/05/2013 6:44 PM, David Levy wrote:
So the science is measuring the star age based on the fundamental Idea
of the Big bang.

Not true, as others have written. In any case, the Big Bang is now
so well supported by so many lines of evidence that using it as a
constraint on star ages is justified.

With the results of the star age they are coming back and reconfirm the
Big bang theory.

Star ages, where they can be measured independently, are consistent
with Big Bang theory, but they are not considered significant
evidence in favor of the Big Bang.

The Steady State model, referred to in a later post, is utterly
dead. The distant universe looks completely different from the local
universe, contrary to the basic Steady State prediction. I suppose
the Big Bang model could turn out to be wrong (though whatever
replaces it will have to look a lot like the Big Bang through the
last 10 or so Gyr), but Steady State is out.

In article ,
Yousuf Khan writes:
[Metallicity] only works for roughly comparing & categorizing really old stars
(mainly first and second generation) vs. modern ones (third generation).

All basically correct but perhaps in need of some clarification.
With few exceptions, there is no mechanism for destroying metals once
created. Therefore, on average, metallicity increases with time. In
the Milky Way, there are no young stars with low metallicity because
the gas out of which stars form has long since been "polluted" with
metals. However, location matters, and young stars formed in the
Galactic outskirts can have lower metallicity than old stars formed
nearer the center.

As Yousuf Khan wrote:
[age-metallicity] is not a linear relationship, you don't have
successive generations of stars getting grittier and grittier.

Basically right, but there aren't strict generations; stars are
forming all the time in the Milky Way.

The galaxies aren't getting more metallic,

Metallicity in individual galaxies is increasing with time but at
different rates in different galaxies.

metallicity is hardly the only way to determine the age of a star,

As (I think) Mike and Martin wrote, metallicity is not a measure of
stellar age except in the crudest approximation. In fact, measuring
ages for individual stars is extremely difficult. Measuring ages for
star clusters is somewhat easier, though. The key is to determine
the mass of the most massive main sequence stars in the cluster, then
use stellar evolution theory to determine the main sequence lifetime
for stars at that mass. Because more massive stars have left the
main sequence, that gives the age of the cluster.

For ages of individual stars, you have to know quite a lot of
detailed information. State of the art is the Sun's age via
helioseismology, but that sort of detail isn't available for many
stars. There are rough indicators such as photospheric lithium
abundance (which decreases with age but reaches zero pretty quickly)
and chromospheric activity, but these are mainly relative indicators
for stars that are otherwise similar.

all stars are 3rd generation now, so metallicity is not the only
way to determine a star's age, nor even the best way.

Basically true for most stars. Some stars are "2nd generation"
(referred to as Population II, but the populations go the opposite
way to generations). Pop II stars have lower metallicity than "3rd
generation" (Pop I) stars, but as I wrote above, there is no direct
relation between metallicity and age for either population.

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