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Hello Amy,
>How long does it take a photon to travel from the center of the sun to
>its surface? I've seen numbers ranging from 30 thousand years to 50
>million years. What gives?
A photon created near the Sun's center bounces around many times
before reaching the Sun's surface, scattered again and again by the
opaque interior of the Sun. The same happens when a piece of metal
conducts heat: the electrons which carry the heat scatter off the
metal atoms so that the heat slowly diffuses through the metal.
Once a photon reaches the base of the Sun's convection zone, 70% of
the way to the Sun's surface, it's carried the rest of the way inside
a rising parcel of gas. Finally the gas expands and cools enough so
it becomes transparent, releasing the photon into space towards us.
The photon's trip through the convection zone takes about 50,000
years. The trip from the center to the base of the convection zone
takes at least a million years, and probably several times more.
Since the photon is gradually degraded during this trip, from an
energetic gamma ray produced by nuclear fusion, to an ordinary photon
of sunlight, our guess at the exact time taken depends on knowing the
opacity for photons of different energies. Because we have no way to
measure in the laboratory the opacity of millions-of-degrees dense
gas, the time to the surface isn't known very accurately.
Best wishes,
-Neal.
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