Core
0–25% of solar radius · Temperature ~15.7 million K · Density 150 g/cm³ · Pressure 265 billion atm · Proton–proton chain fusion converts 600 billion kg H/sec into He · 99% of energy produced within innermost 24% of radius · Photons take 10,000–170,000 years to escape; neutrinos escape in 2.3 seconds

Radiative Zone
0.25–0.70 solar radii · Energy transferred outward by radiation (photon absorption/re-emission) · Photons undergo trillions of scatterings, taking ~170,000 years to cross · Temperature drops from 7 million K to 2 million K · Density from 20,000 to 200 kg/m³ · Plasma too dense for convection

Tachocline
Thin transition layer between radiative and convective zones at ~0.70 solar radii · Large shear layer where differential rotation begins · Believed to be the site of the solar dynamo — where the Sun's magnetic field is generated · Key to understanding the 22-year Hale magnetic cycle

Convective Zone
0.70 radii to surface · Heat carried outward by thermal convection cells (Bénard cells) · Hot plasma rises, cools at surface, sinks back · Creates granulation pattern visible on photosphere · Temperature drops from ~2 million K to ~5,800 K · Mixing time scale ~10 days

Photosphere
Visible "surface" · Temperature ~5,772 K · Only tens to hundreds of km thick · Particle density ~10²³/m³ · Only ~3% ionized · Limb darkening visible · Granulation pattern: ~1,000 km convection cells lasting ~20 minutes · Temperature minimum ~4,100 K at 500 km above surface · Source of most visible light

Chromosphere
~2,000 km thick above photosphere · Temperature rises from 4,100 K to ~20,000 K · Visible as a thin red/pink arc during total solar eclipses (named "color sphere") · Features spicules — jets of plasma shooting 5,000–10,000 km upward at 20 km/s · Hydrogen-alpha emission gives characteristic red color

Transition Region
Very thin layer ~200 km · Temperature jumps dramatically from ~20,000 K to over 1,000,000 K · Complete ionization of helium occurs · Not well-defined altitude — features at different temperatures interleave · Best studied in UV wavelengths from space observatories (IRIS, SDO)

Corona
Outer atmosphere extending millions of km · Temperature 1–2 million K (up to 20 million K in active regions) · Visible during total solar eclipses as pearly white halo · The "coronal heating problem" — why is the corona hundreds of times hotter than the photosphere? — remains an unsolved major problem in astrophysics · Parker Solar Probe crossed the Alfvén surface April 2021 at ~18.8 solar radii