The HR Diagram as a Kingdom

Plate 66 speaks for itself: “Placed by heat and light.”

The Physics

Plotting stars by temperature and luminosity sorts them into the main sequence, giants and white dwarfs. Luminosity, radius and temperature are tied together by the Stefan–Boltzmann law.

L = 4π R² σ T⁴

• L: luminosity, W
• R: stellar radius, m
• σ: Stefan–Boltzmann constant 5.670374×10⁻⁸ W m⁻² K⁻⁴
• T: effective temperature, K

Sun 5772 K. Betelgeuse ≈ 3650 K. Sirius B: 25 193 ± 37 K.

Sources

• IAU 2015 Resolution B3 (nominal solar values).
• H. E. Bond et al., Astrophys. J. 840, 70 (2017).

On the poster

Plate 066, “The HR Diagram as a Kingdom”: the pixel-art plate with its slogan “Placed by heat and light.”, the key equation and the facts panel shown above. Pixelated Physics. Physics. Personified.