Stellar Nursery

Plainly: how big the object is and what colour it would look. The dashed circle is the Sun, drawn for scale. Because real objects here range from white dwarfs the size of Earth to supergiants hundreds of times wider than the Sun, the disk is sized by the logarithm of the radius — each step outward is a factor of ten, not a fixed number of kilometres. A dark grey ball means nothing is burning, so there is no light to give it a colour.

Technically: the drawn radius scales with log R, spanning 10⁻²·⁵ to 10² R_☉. The fill comes from a Planckian-locus approximation to a blackbody at the model's T_eff, with a limb-darkening gradient that is cosmetic rather than computed. The cutaway button shades the left half by T(r) from the solved profile, so you can see how steeply temperature falls from core to surface.

Plainly: the standard chart astronomers use to sort stars — surface temperature across the bottom, total energy output up the side. Both axes are logarithmic, so one step is a factor of ten. Temperature runs backwards, hot on the left, because the chart was drawn that way in 1910 and nobody has fixed it since. The band is where ordinary hydrogen-burning stars live; a dot sitting on it is a normal star, and a dot far off it is something else — a dim dense remnant below, a bloated or unusual object above.

Technically: log T_eff against log L/L_☉, the Hertzsprung–Russell plane. The band is the zero-age main sequence as this solver computes it — the same code run over 0.09 to 250 M_☉ at solar composition, not an observed sequence — so a model that lands off it disagrees with this program's own main sequence, not with the sky.

Plainly: how hot it is at every depth, from the centre on the left to the surface on the right. It is hottest in the middle and falls outward, which is what drives energy out of the star. The dashed lines mark the temperatures where the two hydrogen-burning reactions switch on: if the curve starts above a line, that reaction is running in the core; if the whole curve sits below both, no hydrogen is burning anywhere.

Technically: log T against r/R, with T tied to density by the imposed polytropic stratification T = T_c(ρ/ρ_c)^1/n. Dashed thresholds are the pp onset near 4×10⁶ K and CNO takeover near 1.7×10⁷ K. The outermost points are not physical: this model has no atmosphere, so the curve is just the polytrope running out of gas, and the model's T_eff is nowhere on it.