A little more than two centuries ago, the star system Eta Carinae appeared dimly in the sky. Over the first decades of the 19th century, it grew in brightness, so much so that by the spring of 1843, it was the second brightest star in the sky, behind only Sirius which is about a thousand times closer to Earth. But it grew faint again and by the 20th century was no longer visible to the naked eye. That 19th-century explosion was a "supernova impostor event" -- one of the stars in Eta Carinae came close to a full-blown supernova, but it was not completely destroyed. Although astronomers in 1843 did not have the technology to observe and record the details of the event, the resulting clouds of matter, the Homunculus Nebula, is still visible today, and has been a site of Hubble examination since the telescope was launched in 1990. Above, Hubble's most detailed picture of the nebula to date, released by NASA on February 20, 2012. Scientists believe that eventually Eta Carinae will explode in a true supernova, which will be even brighter than the "impostor event" a century and a half ago.

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Image: NASA.