σ Orionis (blue star), the central ionizing source of IC 434, and its bow wave. The star system consists of a close binary of spectral type O9.5V and B0.5V with a third massive companion (Simón-Díaz et al. 2011), and is moving eastward through the nebula in agreement with the arc direction (white arrow, representing 0.1 Myr of travel time; Perryman et al. 1997). Apparent in imaging in Hα (top left), [O III] (bottom left), WISE 12 μm (top right), and Herschel MIPS 24 μm (bottom right), we see the wind and radiation pressure interacting with the surrounding ISM (Ochsendorf et al. 2014). We further report increased [O III]/Hβ emission (bottom center) but no increase in the gas density as traced by the [S II] line ratio (top center).