The Physics of the Sun and the Gateway to the Stars

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 (⁠$107 K,$ 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 $4×1026 J/s$ 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.