The bright southern variable eta Carinae is one of the most famous examples of a rare class of variable -- the S Doradus or Luminous Blue Variable stars. Eta Car is a giant of a star in all possible senses of the word. Its enormous size and luminosity arise from the fact that it is so massive, perhaps one hundred times the mass of the Sun. Like all massive stars, it is rushing through its core reserves of nuclear fuel far faster than does the Sun, and its life will be measured in millions of years rather than billions. It is likely that eta Carinae will end its life as a supernova within the next few million years.
Eta Car is famous for undergoing several large outbursts during its recorded history, one of which ejected the now familiar shell of material that surrounds it -- the Homunculus Nebula, named after its vaguely human shape. These two large lobes of material were ejected during one of eta Carinae's large eruptions in 1841 (around JD 2390000). The nebula, while beautiful, makes observation and measurement of eta Carinae's brightness a little more challenging. Eta Car has been slowly rising since the 1950s. It's likely to undergo future outbursts too, but when they'll occur, we don't know.