Today's sunshine began its journey tens of thousands of years ago
The light warming your face crossed space in eight minutes, but escaping the Sun's interior took it tens of thousands of years of zigzagging.
Sunlight reaches us almost instantly by cosmic standards. Light travels at about 300,000 kilometres per second, and with the Sun roughly 150 million kilometres away, a photon makes the crossing in about eight minutes. So the Sun you glance at is always eight minutes out of date.
The surprising part is what happens before that final sprint. The energy starts as gamma rays produced by nuclear fusion in the Sun’s dense core. But the core is so crowded that a photon can travel only a tiny distance before slamming into a particle, being absorbed, and re-emitted in a random direction.
This aimless stumble outward — a kind of drunkard’s walk — means the energy takes on the order of tens of thousands of years to claw its way to the surface. Only then does it fly free across space in those eight quick minutes. In other words, the warmth on your skin this afternoon was forged in the Sun long before humans built cities.
Sources & references
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