Complex sentence: Eta Carinae is enclosed by, and lights up, the Homunculus Nebula, a small emission and reflection nebula composed mainly of gas ejected during the Great Eruption event in the mid- 19th century, as well as dust that condensed from the debris.
Split into simpler sentences: Eta Carinae is enclosed by, and lights up, the Homunculus Nebula. The Homunculus Nebula is composed mainly of gas ejected during the Great Eruption event in the mid- 19th century, as well as dust that condensed from the debris.