Eta Carinae nebula. Optical image of the Eta Carinae nebula (NGC 3372, lower center). This is a huge cloud of gas and dust surrounding the wildly erratic variable star Eta Carinae in the constellation Carina. The nebula is over 300 light years across and is lit up by the ionization of its hydrogen gas by radiation from hot, massive stars embedded in it. Dark regions intruding into the nebula are clouds of interstellar dust which absorb the light of the stars and nebula. Eta Carinae itself is a curious star, having reached magnitude -0.8 in 1843, it can become as dim as 8th magnitude.