海山二
Eta Carinae is found within the Carina Nebula, a giant star-forming region in the Carina–Sagittarius Arm of the Milky Way. The nebula is a prominent naked eye object in the southern skies showing a complex mix of emission, reflection and dark nebulosity. Eta Carinae is known to be at the same distance as the Carina Nebula and its spectrum can be seen reflected off various star clouds in the nebula. The appearance of the Carina Nebula, and particularly of the Keyhole region, has changed significantly since it was described by John Herschel over years ago. This is thought to be due to the reduction in ionising radiation from Eta Carinae since the Great Eruption. Prior to the Great Eruption the Eta Carinae system contributed up to 20% of the total ionising flux for the whole Carina Nebula, but that is now mostly blocked by the surrounding gas and dust.