A pedestrian star like the Sun is, in actuality, a physics laboratory we could never build. The Sun is basically a thermonuclear core enclosed in an opaque shroud that insulates the high temperature (107K, or 1 keV) from the cold universe outside. The core is brighter than ten supernovas at maximum light, but the enclosing shroud turns back all but one part in 2×1011 of the thermal radiation, which is largely x rays of 10‐50 nm wavelength. We see only the miniscule 4×1026J/s that leak out. The outward journey of the energy from the core to the surface takes about a million years, illustrating again the immense opacity and thermal capacity of the shroud.

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