A color-first literacy desk: the Harvard sequence O B A F G K M, why hotter stars look bluer (Wien’s law), what “dwarf / giant / supergiant” means, and two life-path cartoons — Sun-like (planetary nebula → white dwarf) and high-mass (supernova → neutron star or black hole). Pair with the nearest-stars yardstick, exoplanets, the local sky chart, and a Milky Way starter.
Educational schematic. Temperatures, masses, and lifetimes are rounded NASA / textbook order-of-magnitude ranges — not a research catalog, not an HR-diagram fit, and not NASA imagery. Sizes on the canvases are exaggerated so the lesson stays visible on a phone.
Interactive · Spectral types
Tap a letter · color follows temperature (hot left)
L / T / Y are brown-dwarf classes — cooler than M, not sustained hydrogen-fusion stars. NASA puts typical brown dwarfs at about 13–80 Jupiter masses.
Yellow Sun, white Sun
Class G is traditionally called yellow, and textbooks still say “yellow dwarf.” From space the Sun looks white: its photosphere is about 5,500 °C (~5,800 K) and the spectrum is broad. Earth’s air scatters blue, so the disk often looks yellow-white from the ground — especially near the horizon. The nickname is literacy, not a paint chip.
Interactive · Life phases
Sun-like path · color and size change with the stage
Interactive · HR cartoon
Hot left · bright up · tap a landmark · not catalog-precise
Literacy · words that keep getting mixed
OBAFGKM
Harvard spectral sequence, hottest to coolest. Mnemonic leftovers exist; the physics is Wien’s law: hotter photospheres peak bluer (often in the ultraviolet), cooler ones redder.
Main sequence
NASA: stars fusing hydrogen to helium in the core — about 90% of the stellar population, from roughly a tenth to ~200 solar masses, living millions to billions of years (the smallest, much longer).
Dwarf / giant / supergiant
Morgan–Keenan luminosity class, not a personality test. V = main-sequence “dwarf” (the Sun is G2V). III = giant. I = supergiant. Same spectral letter can be a compact dwarf or a swollen giant.
Red giant / AGB
After core hydrogen is gone (stars under about eight solar masses), the envelope puffs out. NASA notes red giants often look more orange than red. The asymptotic giant branch is a later, pulsing, mass-losing stage before the planetary nebula.
Planetary nebula
A misleading 18th-century name: not planets. The star’s outer layers drift away as a glowing shell; the leftover core is a white dwarf.
White dwarf
Earth-size remnant, hundreds of thousands of times more massive than Earth. NASA: a teaspoon would outweigh a pickup. No new fusion; it cools for billions of years. The Sun is headed here in about 10 billion years.
Supernova → remnant
Stars about 8–20 solar masses can end in a core-collapse supernova and leave a neutron star (more mass than the Sun packed into a city-scale ball). Still heavier stars can leave a stellar-mass black hole.
Brown dwarfs
Between giant planets and stars. NASA’s teaching range is about 13–80 Jupiter masses. They never settle into sustained core hydrogen fusion the way a main-sequence star does.
Sources · public NASA / ESA / textbook
Cited, not invented
NASA Science — Star basics — birth in molecular clouds, main-sequence fusion, mass vs lifetime, low-mass vs high-mass deaths.
NASA Science — Star types — main sequence (~90%), red giants (<8 M☉), white dwarfs, neutron stars (≈8–20 M☉), black holes (heavier), red dwarfs (~75% of the Milky Way; some ~⅓ M☉ up to ~14 trillion years), brown dwarfs (≈13–80 M_J).
NASA Science — Sun facts — ~4.6 billion years old; photosphere about 10,000 °F / 5,500 °C; about 5 billion years of main-sequence fuel left.
Harvard / Morgan–Keenan spectral types and luminosity classes, and Wien’s displacement law (λT ≈ constant), as taught in standard intro-astronomy textbooks. Temperature bins on this page follow common NASA/textbook OBAFGKM ranges, rounded.
Figures are teaching toys. A real star’s type, mass, and remaining life need spectra and models. This page will not tell you whether Betelgeuse explodes next year. Earthrise preview: NASA / Bill Anders (public domain).