# Q

How long does it take photons to get from the sun to the earth?

### Comments

1. lochaber says

I was going to say something like 8 or 9 minutes, but I didn’t have a source, and was too lazy to check wikipedia (yes, that lazy…)

But Scr…Archivist beat me to it, and had a linky.

2. davehooke says

From the surface of the sun or from nearer the centre? It takes a photon hundreds of thousands of years (on average) to get to the surface. Then the 8 minutes 20 seconds.

From the perspective of the photon, no time passes at all. Relativity.

3. Sunday Afternoon says

@davehooke:

The sun is radiative in the middle and convective nearer the surface: http://science.howstuffworks.com/sun3.htm

But that doesn’t mean that the same photon radiates until the convective zone and then convects to the surface before it leaves the sun. From the link: “Approximately 10^25 absorptions and re-emissions take place in this zone” which, despite what that website says, means that there are around 10^25 photons created/destroyed until the energy gets to the convective zone.

The broad band distribution of photons that we see are mostly from the “black-body temperature” radiation of the surface of the convection layer of sun: http://casa.colorado.edu/~ajsh/colour/Tspectrum.html

If we were instead seeing photons from the centre of the sun released by the fusion reactions, their wavelength would make them gamma-rays: http://www.swpc.noaa.gov/Curric_7-12/Chapter_2.pdf

4. Hj Hornbeck says

Google’s calculator is terribly handy here. At aphelion, it takes 507 seconds, and at perihelion 491. The average is almost exactly 499 seconds. All numbers courtesy the ‘pedia.

As for from the interior to the surface of the sun, “davehooke” nailed the most recent estimate I’ve heard, though they vary widely.

5. birgerjohansson says

Yeah, the estimate I was taught was 4.5 million years from the centre of the sun to the surface. This is actually longer than the time a photon needs to travel from the Andromeda galaxy!