![]() Where c is the speed of light and M is the amount of mass in the sun that is capable of undergoing the above nuclear reactions. Therefore, using Einstein's famous formula E=mc 2 for the conversion between mass and energy we have that the available energy in the sun is: This "missing mass" gets transformed into energy, and this is the energy that causes the sun to shine. ![]() If you look at a periodic table, you will see that one helium atom has a little less mass than four hydrogen atoms combined about 0.7% of the original mass has "disappeared". ![]() We know that the sun shines via nuclear reactions in the core that transform four hydrogen atoms into one helium atom. The total energy that the sun has to burn requires a little extra knowledge (for example, some nuclear physics) to understand. This number can be determined from measurements of how bright the sun appears from Earth as well as its distance from us. The rate at which the sun emits energy (its luminosity) is around 3.8 x 10 26 Watts (that's the number 38 followed by 25 zeroes - quite a lot of lightbulbs!). Lifetime = (energy) / (rate at which sun emits energy) The time for this to occur is roughly the total energy the sun has that can be turned into light, divided by the rate at which the sun is giving off energy, or: This can be estimated by assuming that the sun will "die" when it runs out of energy to keep it shining. The total lifetime of the sun before it becomes a red giant is, as you say, around 10 billion years (meaning that the transition will occur around 5 billion years from now). ![]() It requires a bit more than classical physics, but still, you can estimate the sun's lifetime from a very simple calculation.įirst of all, if you want the current age of the sun (around 5 billion years) this number is determined from radioactive dating of objects in the solar system which are known to have formed around the same time as the sun, as stated in the answer to a previous question. How can I calculate the age of the sun using classical physics? I know it's estimated to have a life of about 10 billion years, but was this calculated? ![]()
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