16th Jan 2014

Slow Light

It takes a photon just eight minutes to traverse the 150 million kilometres between the Earth and the Sun, but a photon in the core of the Sun will travel only thirteen centimetres in that same time.

Stars are essentially huge nuclear fusion factories, forging elements in their incredibly hot cores. X-rays and Gamma rays are emitted as a byproduct of this process, but their movements to the surface aren’t straight or easy—the journey could take them tens of thousands of years. The Sun’s core is so dense that the radiation continually hits other atoms, travelling only a few millimetres before being absorbed and then re-emitted over and over again, zig-zagging its way out like a drunk staggering home.

Slowly, the photons work their way up through various layers, including the radiative zone, where they are remitted at longer wavelengths and therefore gradually converted to visible light. Then they pass through the convective zone where the photons are absorbed by gas, heating it up and making it rise towards the surface where it creates the boiling effect we recognise so well.

Finally, after travelling 695,000 kilometres from the core, the photons burst free of the photosphere and into the vacuum of space, racing off at the ordinary speed of light: 300,000 kilometres per second.

It might seem like we’re getting fresh, new light down here on Earth, but in reality our skin is being kissed by photons born eons ago.

(Image Credit: NASA)

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