An Ancient Universe: How Astronomers Know the Vast Scale of Cosmic Time
THE ANCIENT UNIVERSE
b) The Age of the Oldest Stars
Other stars may have different lifetimes. Stars smaller (less massive) than the Sun have longer lives because they fuse their hydrogen fuel so much more slowly. Similarly, a sub-compact car may have a smaller gas tank than a large SUV, but it may be able to drive much longer on a full tank of gas, because it uses its fuel much more slowly.
When a star has used up the available hydrogen fuel in its center, it expands and becomes a "red giant". Once we have found such a giant star, we know that it has used up all its hydrogen. If we can estimate its initial mass, and hence its initial power, we can estimate its lifetime, and we therefore know its age. This is equivalent to saying that, if we see a car that has just run out of gas, and if we know its horsepower, fuel efficiency, and fuel capacity, we can figure out how long it had been driving since the last fill-up before it ran out of gas.
In this way, we can measure the ages of certain stars. When we apply this method to the oldest stars we can find, we obtain ages of 10 - 15 billion years.
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An Ancient Universe - Table of Contents
Home | Introduction | The Universe: An Overview | The Process of Science | The Ancient Universe - The Age of the Expanding Universe - The Age of the Oldest Stars - The Age of Light From Distant Galaxies - The Age of the Chemical Elements | The Changing Universe - Changes in the Solar System - Changes in Stars - Changes in the Universe | Science and Religion | Resource Guide | Activities
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