Wolf-Rayet nebula NGC 2359. Wolf-Rayet (WR) nebulae comprise gas ejected by a very hot central star (not seen), glowing as it is ionised by the star's radiation. The ejection of this gas, primarily hydrogen, exposes the inner parts of the star, composed of the products of the nuclear reactions which power it. The two main types of WR star contain helium and nitrogen (WN stars, such as this) or helium, carbon and oxygen (WC stars). WR stars may be a million times more luminous than the Sun, and lose mass 100 times faster than comparably luminous stars. NGC 2359 lies around 40,000 light years from Earth in the constellation Canis Major.