A nebula is a glowing cloud of gas and dust where new stars are born. The Orion nebula, a planetary nebula, photograph the nebula.
The colours in photographs are real but not what an eye would see: the gas glows in particular wavelengths and long exposures collect what the eye cannot. A planetary nebula has nothing to do with planets — it is a dying star's shed outer layers, and the name is a mistake that stuck.
1nounnebulaA glowing cloud of gas and dust in space.
“Through the telescope, the nebula looked like a faint pink cloud among the stars.”
nebula is a cloud in space.
Latin nebula means mist or cloud, related to Greek nephele, a cloud, and German Nebel, mist.
Latin
nebula — little cloud, mist
English, today
nebula
Learned borrowing from Latin nebula (“little cloud, mist”). Akin to Ancient Greek νεφέλη (“cloud”), German Nebel (“mist, nebula”), Old Norse nifl, Polish niebo (“sky, heaven”), Russian не́бо (“sky”).
Etymology from Wiktionary, CC BY-SA