That's the title of a favorite miniseries on the Science channel on TV. sci2.tv
It seldom tells me much I didn't already know, but it's less boring than your average sitcom.
One recent episode treats of a surprising property of solar radiation, which I already knew about, but treats it in a little more detail.
One commentator is the well-known astrophysicist and astronomer Alexei Filippenko en.wikipedia.org/wiki/Alexei_F…
whose course on astronomy I had watched on DVD. It was good to see him again, but I found his comments on the topic of this show highly objectionable. He spoke of a photon originating near the center of the sun "wanting" to get to the surface. Photons don't have desires, they just follow physical law.
The "surprising property" is that a photon originating in a nuclear fusion reaction near the center of the sun takes a very long time to reach the surface, because it is impeded by the extremely dense plasma in the core. It takes, on average, perhaps 100,000 years to exit the radiative zone, another week or two to propagate up through the convection zone to reach the photosphere -- i.e. what we see as the shining surface of the sun.
The reason it takes so long is that the path a given photon follows is what is known as a "random walk" en.wikipedia.org/wiki/Random_w…
. The photon is emitted from a fusion event, almost immediately absorbed by an electron or proton of the plasma and re-emitted (perhaps as several photons) in a random direction and again almost immediately absorbed, etc. The path it follows is thus unpredictable, but the "expected" i.e. average distance from the starting point increases uniformly, though very slowly, as time passes.
Once the photon or its progeny reaches the photosphere, it takes only about 500 seconds -- a little over 8 minutes -- to travel 150 million kilometers, the distance from Sun to Earth. It will in all likelihood miss the Earth, as Earth is quite small compared to the surface area of a sphere of radius 150 million km.
There is not, as the narrator suggested, any maximum residence time for the photon within the sun. It is entirely possible that there are some photons that have been bouncing around inside the sun for the whole 4.5 billion years since the sun started to shine, though the percentage in that cohort must be pretty small.