The sun will last, at its current brightness for 9 billion more years. How long until the sun gets burned down to the point where it cannot sustain life on earth anymore? I am more. The sun's spectrum is very complex, and indeed there are a lot of lines—both light and dark (emission and absorption)—amidst a sea of what looks to be continuous frequencies. The sun's energy comes primarily from fusion of light elements in its core.
It is estimated that a very small fraction of mass of the sun (~$10^{-12}$ times the abundance of hydrogen) is. The photons take thousands of years to fight their way to the surface of the sun, but then escape into space as visible or near visible photons at the speed of light. I am really confused. I want to know how much lux the sun emits on a bright day - i don't mean when one stares directly at the sun, but rather when one walks casually outside when the sun is shinning brightly.
