Light from the sun takes a mere eight minutes to travel to Earth across nearly 100 million miles of empty space. But it takes 120,000 years to travel just 400,000 miles from its origin in the sun’s core to its surface.

A photon, one of countless trillions upon trillions of photons ejected from the sun, is born in the core of the sun from the fusion of hydrogen into helium.

Matter in the sun is in the form of plasma, naked protons and electrons. Hydrogen is overwhelmingly the most abundant element, essentially a single naked proton. Fusion occurs when protons collide hard enough to overcome their electrostatic repulsion. In the sun’s core, this takes place at a temperature of 16 million degrees and pressure of 250 billion atmospheres.

The strong force is so named because it is strong enough to overcome the electromagnetic repulsion of the positively charged protons. The strong force acts over only extremely small distances, so in order to get two protons to fuse, they must be traveling very fast and under tremendous pressure.

The core of a star is the only place in the universe where such conditions exist.

When the strong force fuses two protons, the resulting bundle has less mass than the two individual protons. The excess mass converts to energy in the form of a gamma ray photon.

If gamma photons could make it to the surface of the sun and escape into space, the sun would glow in deadly gamma rays instead of visible light.

Lucky for us, the photons must travel through nearly half a million miles of rugged territory in the interior of the sun, which robs them of energy before they emerge from the sun’s surface.

Once the energetic gamma photon leaves the sun’s core, it encounters a 300,000-mile-thick radiative zone. Here the plasma is denser than lead and cools to a mere 360,000 degrees at the top.

From the photon’s point of view, traversing the radiative zone is like trying to run across a packed dance floor: It keeps running into protons. With each collision, its progress is slowed as it is absorbed and re-emitted with less energy. By the time it reaches the top of the radiative zone 100,000 years later, it only has one ten-millionth of its original energy and is now an X-ray photon.

Then it enters the 120,000-mile-thick convection zone, which is a frothing, seething cauldron of turbulent plasma, like a lava lamp on steroids. Our photon hitches a ride upward in the froth, and about a week later it emerges as a visible photon into the photosphere, now having only one one-millionth of its X-ray energy.

The photosphere is the inner atmosphere of the sun, the part that we see, but the photon’s journey is not over yet. The photosphere is a region of magnetic mayhem as the sun’s rotation twists the magnetic field lines into a tangled mess that can trap the photon beneath a sunspot.

Imagine, the light reaching our eyes today started its journey in the sun’s core long before humankind left the savannas of Africa 60,000 to 80,000 years ago.

Richard Brill is a retired professor of science at Honolulu Community College. His column runs on the first and third Fridays of the month. Email questions and comments to brill@hawaii.edu.