A hypergiant irregular variable, which became the second brightest star in the sky (magnitude −0.8) in 1843. Its current magnitude is around 5.5, but it shows fluctuations over periods of decades. It is a luminous blue variable of absolute magnitude −10, and is officially classified as an S Doradus star. It lies inside a cluster of massive stars. It is now thought to be a massive binary with an orbital period of 5.5 years and an eccentricity of about 0.75. The only spectrum visible is that of the surrounding Homunculus Nebula. Eta Carinae is an intense infrared source and its extreme mass loss (about 0.1 solar masses per year) involves energies close to those of some supernovae. It lies about 7500 l.y. away.
Subjects: Astronomy and Astrophysics.