Full width at half maximum (FWHM) of A3’s dust tail as a function of angular distance from the nucleus. Horizontal error bars denote the span of distances along the tail used in determining the FWHM, while vertical error bars reflect the measurement uncertainties in the FWHM profiles. The black solid lines indicate the best-fit relation, θ_⊥ ∝ l^1/2, linking the tail’s FWHM to its distance from the nucleus. Derived dust ejection velocities are v_⊥ ~ (68 ± 4)β^1/2 m s⁻¹ to the east and v_⊥ ~ (61 ± 5)β^1/2 m s⁻¹ to the west.