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Name: Tony
Status: other
Grade: other
Location: NV
Country: N/A
Date: N/A

How do we know the sun's age?

Hi Tony,

There are two important ways that the age of a star, such as our Sun, can be determined. The first and more well known process is by observing other stars and making a kind of tally as to its mass, brightness, chemical composition, etc. From so many observations, a "stellar evolution" pattern can be developed.

For example, since we understand that the main source of solar energy is hydrogen fusion, it follows that a young star should have quite a bit of hydrogen in it, whereas an older star would have more helium (the product of hydrogen fusion). If we then arrange the observed stars in terms of how much hydrogen, helium, and other chemicals it might have, we also see other trends - such as stars with originally about the same mass as the Sun tend to become red dwarfs when most of its hydrogen gets used up.

So, in the first process, we make a very strong estimate of the age of a star by observing a lot of other stars and using that data to develop a "life-cycle" of stars. Then all we have to do is determine where in that cycle is our own Sun and that tells us its age.

In the second, newer, process, we use our knowledge of radioactivity and the patterns of production and development of radioactive materials (we know for example that a sample of C-14 will become half its current concentration after 5730 years) to get an estimate about the age of objects in our solar system. It turns out that the oldest known objects have the same approximate age as that of the best estimates of the Sun's age.

So these two processes come up to the same conclusion that the Sun is about 4.5 billion years old.

Greg (Roberto Gregorius)
Canisius College

We can estimate the Sun's age by studying its behavior. It takes about 5 billion years for a star like ours to behave as our Sun does. If it were much younger, it would be much hotter; cooler as it gets much older. We can also compare the Sun to other stars like it.

Studying the Sun's spectrum also gives us an idea of its age.

Hope this helps!

David Levy

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