Why were expanding shells of ejected stellar material historically named 'planetary nebulae'?

Answer

Early telescopes made them look somewhat like faint planets

The term arose because early telescopes gave these glowing, expanding shells an appearance somewhat similar to faint planets, though they are unrelated to planets.

Why were expanding shells of ejected stellar material historically named 'planetary nebulae'?

#Videos

Why Do Red Giant Stars Expand Their Outer Layers? - YouTube

evolutionlayerstarexpansionastrophysics