The Eta Carina Nebula is the largest diffuse nebula in the sky, much larger
than the more famous Orion Nebula; that it is not
better known is no doubt due to the fact that it is not
visible from most of the Northern Hemisphere.
The star Eta Carinae itself is also interesting.
It is a variable star; in the mid-19th century it was the second brightest
star in the sky; today it is not even visible with the naked eye.
It is an extremely large star (150 times the mass of the Sun and 4 million times
brighter). Such large stars are very unstable.
Eta Carinae's most recent outburst in 1841
expelled the gas that creates the spectacular nebula
(sometimes called the Homunculus Nebula) that we see today.
The bright lobes of the nebula are about the same size as our
whole solar system.
The images on the left below are of Eta Carinae and the Homunculus Nebulae.
The extraordinary clarity of the HST image allows us to study this fascinating
region in much more detail.
The images on the right below are of the whole Eta Carina Nebula (which
also includes the Keyhole Nebula).