A picture of the sun, taken with a neutrino detector, at night through the Earth

News to me too. I found a site. The answer is longish but begins this way:

A photon of light can take 100,000 years from the core of the Sun to get to the surface.

the density of the core is incredibly high — 150 times greater than water. So all the atoms are jammed up against each other.

Let's look at a pair of hydrogen atoms that have fused together to make a helium atom — and released a lot of energy, in the form of gamma rays. The gamma rays can travel only a few millimeters, before they're absorbed by an atom, and then re-radiated.

Over and over again, they are absorbed, and then re-radiated. So, very slowly, the gamma-rays that have been generated by nuclear burning work their way up from the dense core.

After thousands upon thousands of years, they make their way into what's called the 'radiative zone'. The radiative zone is huge — it stretches up from the outer core (that's at the 24 per cent mark) to about 70 per cent of the way to the surface.

It's called the radiative zone, because here, energy travels by radiation. The gamma rays are still being absorbed and re-radiated, but each time they're being re-radiated at longer wavelengths. They gradually get converted from gamma rays down to visible light.

ref: https://www.abc.net.au/science/articles/2012/04/24/3483573.h...

> Once a photon of light is born, it travels at a speed of 300,000 km/sec until it collides with a charged particle and is diverted in another direction. Because the density of the sun decreases by tens of thousands of times from its lead-dense core to its tenuous photosphere, the typical distance a photon can travel between charged particles changes from 0.01 cm at the core to 0.3 cm near the surface.

[0] https://sunearthday.nasa.gov/2007/locations/ttt_sunlight.php

> What? Why?

I had the same question, and it looks like there's lots of variation with the number. For instance, this website (https://scied.ucar.edu/learning-zone/sun-space-weather/insid...) says it takes "millions of years."

Also, has anyone though of how mind-numbingly wasteful solar fusion is? All that energy, and only a tiny fraction makes it to Earth with the rest getting dumped wastefully into space. Seems like an area that's ripe for disruption by a startup.

But he also writes this:

> Since the Sun’s light was made at the height of the last Ice Age, for all we know its nuclear fires could have gone out 29,000 years ago.

Which makes me even more confused.