Thomson Cross Section

The effective target area of an electron scattering light at low energy.

Specifications & Metrics

symbol

σe

status

Measured — CODATA 2022 adjustment

value

6.6524587051 × 10⁻²⁹ ± 6.2 × 10⁻³⁸ m²

Relative Scale in Constants

Core Principles & Analysis

• About 6.65 × 10⁻²⁹ m² — small, but multiplied by whole stars.
• Sets the opacity of stellar interiors and the depth of the solar photosphere.
• Grows at high photon energy into Compton and Klein–Nishina scattering.