Eta Carinae Nebula. Optical image of the Eta Carinae Nebula (NGC 3372), 6500 light years away from the Earth. It is classified as a HII region; it is an enormous cloud of hydrogen gas 300 light years across, which is ionised and lit up by the ultraviolet radiation of two clusters of young, hot stars. The dark regions in the nebula are clouds of interstellar dust which absorb the light emitted by stars in these areas. At upper centre left, in the bright part of the nebula, lies the star Eta Carinae (not identifiable here). It exploded in 1843 to become one of the brightest stars in the sky for a few years.