Why were expanding, glowing shells of ionized gas shed by dying stars historically named Planetary Nebulae?

Answer

They resembled planets like Uranus or Neptune during early telescope observations

The term Planetary Nebula arose because early astronomers observing these roundish objects with primitive telescopes mistook their appearance for that of planets like Uranus or Neptune.

Why were expanding, glowing shells of ionized gas shed by dying stars historically named Planetary Nebulae?

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How Stars Die - YouTube

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