Delta Cephei is emitting around 2,000 times the Sun's luminosity. This is producing a strong stellar wind, which, with the pulsations and shocks in the star's atmosphere, is ejecting mass at the rate of masses per year. This is the equivalent to the mass of the Sun roughly every million years. The matter is flowing outward at a velocity of about 350 km s. This expelled gas forms a nebula about one parsec across, centered on Delta Cephei, and contains 0.07–0.21 solar masses of neutral hydrogen. A bow shock is being formed where the stellar wind is colliding with the surrounding interstellar medium.