This page plots a smooth, schematic Hertzsprung–Russell evolutionary track for a roughly one solar-mass star at metallicity Z = 0.02 (near-solar composition). The horizontal axis is log₁₀ of effective surface temperature with hotter stars to the left, matching common observational HR conventions; the vertical axis is log₁₀ luminosity in solar units. Normalized age u ∈ [0, 1] is a compressed timeline: most of u is spent near the zero-age main sequence, while helium burning, the asymptotic giant branch, and post-AGB transitions occupy narrow ranges of u for visibility. The track is a hand-designed spline through qualitative phases (main sequence, Hertzsprung gap / subgiant, red giant branch, a cartoon horizontal-branch excursion, AGB, post-AGB, white dwarf cooling) and is not output from a stellar-evolution code such as MESA or PARSEC. Students should compare against the separate static HR “regions” page and treat numerical T_eff and L as pedagogical guides only.
Who it's for: Introductory stellar astrophysics after the static HR diagram; pairs with nuclear binding, Chandrasekhar, and neutron-star TOV pages.
Key terms
Hertzsprung–Russell diagram
main sequence
red giant branch
horizontal branch
asymptotic giant branch
white dwarf
metallicity
How it works
A schematic Hertzsprung–Russell track for a ~1 M☉ star at metallicity Z = 0.02 (roughly solar): long main sequence, subgiant rise, red giant branch, a cartoon core-helium excursion (horizontal branch), asymptotic giant branch, a rapid post-AGB crossing, then white dwarf cooling toward lower luminosity. Normalized age along the abscissa is not calibrated to gigayears — it compresses post-main-sequence phases for visibility. This is not a MESA / PARSEC model; it is a smooth teaching spline for orientation next to the static HR regions page.
Frequently asked questions
Why does the star spend almost all of the slider on the main sequence?
A ~1 M☉ star’s hydrogen-burning lifetime is orders of magnitude longer than later phases; the normalized age u is chosen to stretch post-main-sequence evolution so RGB/AGB/WD are visible on one control.
Is the horizontal branch realistic?
Only schematic. Real HB morphology depends on mass loss, metallicity, mixing, and clusters vs field stars; here a short blueward hook illustrates core-helium ignition without fitting globular-cluster tracks.