Doppler Effect

Shift in observed frequency when source and observer move relative to each other, from sirens to redshift.

Core Principles & Analysis

• Christian Doppler proposed it in 1842 to explain the colors of binary stars.
• Buys Ballot tested it in 1845 with trumpeters playing on a moving train while musicians judged the pitch.
• Its relativistic form underlies cosmological redshift, radar speed guns, and medical ultrasound.

Specifications & Metrics

• SYMBOL: f′ = f·(v ± v₀)/(v ∓ vₛ)