Science & Technology

# That Sunlight You Feel Might Be 50 Million Years Old

Everybody knows that nothing is faster than light. And everybody knows that it whooshes through the solar system in a matter of minutes (well, technically, it takes just over five hours for light to travel from the sun to Pluto). But here's something you might not know — the light that reaches Earth might have been created at the center of the sun more than 50 million years ago.

## Getting Lit

Light travels 186,388 miles per second, and on average, the Earth is 92.96 million miles away from the sun. If you run the numbers, that works out to be about 8.31 minutes from the moment that light leaves the sun to the moment it starts charging your pocket calculator. It's kind of weird to think that if the sun disappeared, we wouldn't even realize it for eight minutes. But it's even weirder to think that those same light waves have probably been kicking around inside the sun for tens of thousands (or even millions) of years beforehand.

The radius of the sun is about 432,000 miles (695,000 kilometers) — a distance that light can travel in two seconds and change. But inside the sun, the photons, or light particles, don't make a straight dash, so it takes considerably longer. Instead, they take a path that's known as the "drunkard's walk." Imagine a man who's so drunk he can't walk in a straight line. He's leaning on one lamppost, and he just wants to get to the next one. But every time he takes a step, it's in a random direction. To calculate how long it will take for him to get to his destination, you take the number of steps that it would normally take (let's say it's 10) and square it. So after 100 meandering steps, he'll finally make it to his next stop. That's how every photon travels from the sun's core to its photosphere.

## Light Finds a Way

But there aren't a lot of lampposts on the sun, nor is it known for its raging bar scene. So what's actually going on up there? It all starts in the core, where billions of hydrogen atoms fuse with each other to create helium. This process creates two types of particles: neutrinos, which are elementary particles that barely interact with physical matter at all, and gamma rays, which are high-energy photons that interact with matter in a big way. The neutrinos shoot through the sun no problem, but every time the gamma-rays collide with an atom, they are absorbed and re-emitted in a random direction.

If you're researching how long it will actually take for an average photon to get from the core of the sun to your sweet shades, then you're out of luck — the answers are always vague, and range from 10 thousand to 50 million years. It's a drunkard's walk, remember? Actually doing such a calculation would be very complex and wouldn't have much use, so nobody's spent much energy on it. But it all comes down to the length of our photon's drunken "step." If that distance is a centimeter, then the photon will make it to Earth in a measly 5,000 years. But if it's a half a millimeter, then the journey will take a half a million years. Until we know exactly how dense it is at the core, we'll never know the answer for sure.

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For a dramatic tale of science and destruction, check out "The Sun Kings: The Unexpected Tragedy of Richard Carrington and the Tale of How Modern Astronomy Began" by Stuart Clark. We handpick reading recommendations we think you may like. If you choose to make a purchase, Curiosity will get a share of the sale.

Reuben Westmaas