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H-R Diagram & Stellar Classification Lab

Build your own Hertzsprung-Russell diagram by adjusting star temperature, radius, and mass. See how the Stefan-Boltzmann law determines luminosity, classify stars by spectral type (OBAFGKM), and explore the main sequence, giant branch, supergiant region, and white dwarf corner of the diagram.

Guided Experiment: Mapping the Main Sequence

How do temperature, luminosity, and mass relate for main-sequence stars? Predict where cool, dim stars and hot, bright stars will appear on the H-R diagram.

Write your hypothesis in the Lab Report panel, then click Next.

Hertzsprung-Russell Diagram

SupergiantsGiantsMain SequenceWhite Dwarfs3k5k10k20k40k10⁻⁴10⁻²10⁰10²10⁴10⁶Temperature (K) — hot ← → coolLuminosity (L☉)OBAFGKMSunSiriusBetelgeuseRigelProxima CentauriVegaAldebaranSirius B

Controls

2,000 K40,000 K
0.01 R☉1,000 R☉
0.08 M☉100 M☉

Star Properties

Spectral Class G
Yellow
Main Sequence
Luminosity
1 L☉
L=4πR2σT4L = 4\pi R^2 \sigma T^4
Absolute Magnitude
4.83 mag
Mabs=M⊙−2.5 log⁡10(L/L⊙)M_{\mathrm{abs}} = M_{\odot} - 2.5\,\log_{10}(L/L_{\odot})
Estimated Lifetime
10.0 billion yr
t≈1010(M⊙M)2.5 yrt \approx 10^{10} \left(\frac{M_{\odot}}{M}\right)^{2.5} \text{ yr}
Temperature
5,778 K
Radius
1 R☉
Mass
1 M☉

Data Table

(0 rows)
#Star NameTemperature (K)Radius (R☉)Luminosity (L☉)Spectral ClassRegion
0 / 500
0 / 500
0 / 500

Reference Guide

The H-R Diagram

The Hertzsprung-Russell diagram plots stellar luminosity against surface temperature. Hot, bright stars appear in the upper left while cool, dim stars occupy the lower right.

About 90% of all stars fall along the main sequence, a diagonal band where hydrogen fusion powers the star. Stars spend most of their lives here before evolving into giants, supergiants, or white dwarfs.

The diagram is one of the most important tools in astrophysics, revealing how stellar mass governs temperature, luminosity, color, and lifetime.

Spectral Classification

Stars are classified by surface temperature into spectral types O, B, A, F, G, K, M (often remembered as "Oh Be A Fine Girl/Guy, Kiss Me").

  • O (>30,000 K) — Blue, very hot, massive, short-lived
  • B (10,000-30,000 K) — Blue-white
  • A (7,500-10,000 K) — White (e.g. Sirius, Vega)
  • F (6,000-7,500 K) — Yellow-white
  • G (5,200-6,000 K) — Yellow (e.g. the Sun)
  • K (3,700-5,200 K) — Orange
  • M (<3,700 K) — Red, coolest, most common

Stefan-Boltzmann Law

A star's luminosity depends on its surface temperature and radius through the Stefan-Boltzmann law.

L=4πR2σT4L = 4\pi R^2 \sigma T^4

Here L is luminosity, R is the stellar radius, T is the effective surface temperature, and σ is the Stefan-Boltzmann constant (5.67 × 10⁻⁸ W m⁻² K⁻⁴).

This explains why a cool red giant (large R, moderate T) can outshine a hot main-sequence star, and why a hot white dwarf (tiny R, high T) can be very dim.

Stellar Lifetime

A star's fuel supply (mass) and burn rate (luminosity) determine how long it shines. More massive stars burn through hydrogen far faster than less massive ones.

t≈1010(M⊙M)2.5 yearst \approx 10^{10} \left(\frac{M_{\odot}}{M}\right)^{2.5} \text{ years}

The Sun will last about 10 billion years. A 10 M☉ star burns out in roughly 30 million years, while a 0.1 M☉ red dwarf can shine for trillions of years, far longer than the current age of the universe.