About 170 years ago, a star nearly exploded in the Southern constellation Carina.  I say nearly for a few reasons.  On Earth, observers saw a dim, seemingly-average star become the second brightest star in the night sky.  It stayed that way for 20 years before slowly fading. When we looked at it with telescopes, we found that whatever happened to Eta Carinae, it ejected more than 30 times the mass of our Sun in that short twenty year period, creating what we now call the homunculus nebula. Eta Carinae is a multiple star system 7500 light years away from Earth, so rest assured any...