Eta Carinae's great eruption in the 1840s created the billowing Homunculus Nebula, imaged here by Hubble. Now about a light-year long, the expanding cloud contains enough material to make at least 10 copies of our sun. Astronomers cannot yet explain what caused this eruption. Image Credit: NASA, ESA, and the Hubble SM4 ERO Team

Eta Carinae is the most luminous and massive stellar system within 10,000 light-years of Earth (the distance light travels in 10,000 years).

It is known for its surprising behavior, erupting twice in the 19th century for reasons scientists still don’t understand.

It is actually made up of two massive stars whose oval orbits bring them close together every five and a half years.

The brighter, cooler primary star has about 90 times the mass of our sun and is 5 million times brighter.