How Long Will the Sun Shine?

Sun Image

We once thought the Sun an unchanging and perfect sphere. In the 1600's, Galileo discovered sunspots on the Sun, forever changing that perspective. Even early astronomers who knew the Sun was a ball of gas, thought it was a pretty static system. In our century,with all our satellites and instruments we now know the Sun is a very active place, with violent eruptions and phenomenon we are still trying to understand.

Stars like the Sun (we call them G class stars) create enormous amounts of energy by converting hydrogen into helium. The nuclear furnace takes place in the solar core where temperatures are 15 million degrees Kelvin and pressures are 151 g/cm3, more than 13 times more dense than solid lead! With these temperatures and pressure, fusion can take place. It's the only place in the Sun where this happens.

So when the Sun converts hydrogen to helium, it's losing mass. How fast? Every second, the Sun converts about 700 million tons of hydrogen into helium. Although it would seem that the Sun is losing an awful lot of mass very quickly,it's really insignificant when you think about the Sun being 100 times the diameter of the Earth and 333,000 times the mass. In the 5 billion years the Sun has been burning it has consumed only a few hundreds of one percent of its total mass!

But, all good things come to an end and the Sun and its life giving energy is no exception, but don't worry it's a long, long way away! Astronomers think the Sun will quietly end its life as a white dwarf in about seven billion years. Before that though, several events will occur. Current models show the Sun will use up all the hydrogen in its core, gravity will take over, causing the Sun to collapse.

The collapse will cause the Sun to heat up again and burn the little bit of hydrogen that was left around the core. When this happens, the Sun will swell into a red giant star. Now the Sun's core will heat up again and it will burn its helium and the Sun will shrink and swell several times until it finally collapses into a white dwarf.

As the Sun swells to a red giant, it will engulf earth, vaporizing our planet, but by then, life will have long ago disappeared. Models show that the Sun will be increasing in luminosity, and in about a billion years, the Sun will be 1.4 times more luminous than it is now. This will cause Earth to be in a greenhouse state. Our oceans will evaporate into the atmosphere and after that, Earth will experience a permanent runaway greenhouse effect much like that on Venus. Let's hope by then we've achieved interstellar spaceflight!