INTRODUCTION

1. Ancient people and the Sun
2. What happens when the Sun's lights goes out?
3. Why is the Sun important to life on Earth?
4. How long will the Sun last?

How long will the Sun last?

Astrophysicists estimate that the Sun will begin to expand as it runs out of hydrogen fuel in its core in about 4-5 billion years from now, entering the red giant stage of a sun's development (SOHO). The Sun has already existed about 4.5 billion years. Although the Sun may exist beyond this time as a white dwarf, it is unlikely that Earth will be a nice place to live if it exists at all.

... from Dr. SOHO FAQ
"How many years will it take before the Sun explodes or disappears?

Here is the short answer:
Four to five billion years (4-5,000,000,000 years)

The Long Answer:
The Sun will not explode; it is too small to "go nova." It WILL expand as it fuses the last of its core hydrogen. The outer layers of gas will swallow some inner planets (possibly even the Earth). Then the inner parts of the Sun will stop fusing, contract, and become a white dwarf. It will remain a small, hot, slowly- cooling dwarf for many tens of billions of years after that. (It will have most of the heat of a full-sized star, but only a tiny surface area with which to radiate it. Therefore, it will take a very long time to cool down. This will not help us; it will be too cold to support life on Earth by then, even if the Earth could survive the red giant phase.) Scientists based this picture of the Sun's future on the basic nuclear reactions in a star's core. The rates of these reactions depend upon the mass of the star. (smaller stars burn more slowly, and thus longer, than more massive ones, but I could be oversimplifying things.) Scientists use planetary orbits and the laws of orbital dynamics to estimate the mass of the Sun. So, with the mass of the Sun and the rate at which this mass is consumed by fusion, we can guess that the Sun's lifetime will be 9 billion or 10 billion years, total. We know (from Earth's geology and Moon rocks, for example) that the age of the solar system is 4.5 or 4.6 billion years. We think the planets formed at roughly the same time as the Sun. Therefore, based on current scientific theory, the Sun will expand in four or five billion years."

To think About:

To explore: