MadSci Network: Physics

Re: At what rate does the sun burn out and in how many years will it be gone?

Area: Physics
Posted By: David Barlow, Private individual, Grad education in Physics/Astrophysics and Comp. Support
Date: Tue Jan 21 23:19:04 1997

Dear Chantal

These questions are closely linked. How long the Sun will last depends on how fast it burns, as I sure you have guessed. How long it burns for will depend on what it burns and how it does so. So, another good question to ask is what does the Sun burn, how does it do it and how much of it is there to burn.

First I will answer your question then answer my own question. The Sun will last about 5 billion years as it is now, a so called Main Sequence Star, and burns 700 billion tonnes a second. This may look like a lot but the Sun actually burns Hydrogen, a gas, and it turns it into Helium, another gas. This happens in the central part of the Sun, its Core, through a process called nuclear fusion. A side effect of fusion is that light and heat are created. So only a small amount of this Hydrogen, only a few Billion tonnes a second, is actually burned off to create light. I would not worry that so much Hydrogen is burnt every second as the sun has a mass of 1.989 times 1030Kg. That is 1,989,000,000,000,000,000,000,000,000,000,000 Kg, or one million nine thousand, eight hundred and nine billion, billion, billion Kg. So the odd few Billion tonnes will not be missed.

What is really interesting is what happens after the Hydrogen has been used up in the Suns core. At this point in our Sun's life the central part of the Sun, its core, shrinks and heats up and its atmosphere will expand to cover the Earth, and possibly Mars. The Sun is now called a Red Giant Star. If you can find the constellation Orion, the bright red star in the upper left hand corner is a Red Giant called Betelgeuse. After only a few million years the core will shrink again and the our Suns atmosphere will be blown off into space to become Planetary Nebulae. What will be left is a type of Star called a White Dwarf. This will last for many tens of billions of years, slowly cooling and getting dimmer. So, our star, the Sun, will last for 5 Billion years as it is, a few million years as a Red Giant, and finally tens of Billions of Years as a White Dwarf.

To find out more about the Sun, and some of the background to this, follow the links below.

•The nine planets, plenty of links to other sites about the Sun.
More about the Sun

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