Leavitt's Law

Plate 70 speaks for itself: “Slow is bright.”

The Physics

Henrietta Leavitt found that Cepheid variables with longer pulsation periods are more luminous. Calibrated, the period gives the true brightness, turning Cepheids into distance markers.

M_V = a log₁₀ P + b

• M_V: absolute visual magnitude, dimensionless
• P: pulsation period, days
• a, b: calibration constants

Longer-period Cepheids are brighter. M_V = −2.43(log P − 1) − 4.05.

Sources

• H. S. Leavitt, E. C. Pickering, Harvard Coll. Obs. Circ. 173 (1912).
• G. F. Benedict et al., Astron. J. 133, 1810 (2007).

On the poster

Plate 070, “Leavitt's Law”: the pixel-art plate with its slogan “Slow is bright.”, the key equation and the facts panel shown above. Pixelated Physics. Physics. Personified.