Planetary Nebula14.9 - Understand the principal stages and timescales of stellar evolution for stars of similar mass to the Sun, including:
c) planetary nebula
Planetary Nebula is a misleading name. Originally they were thought to be a region around a star where planets would form. This is not the case, quite the opposite in fact.
When a red giant expels its outer layers before becoming a white dwarf or neutron star, the layers become a thin sheet of gas around the remains.
Their shape and colour depend on the size, composition of the Sun and its direction to us from Earth. Planetary Nebula can range from the width of the Solar System to more than a light year wide.
There are many good examples of planetary nebulae, some are beautiful, some are eerie and some are quite funny such as the Clownface Nebula in Gemini.
Supernova remnants are similar to planetary nebulae only caused by a supernova and usually more cataclysmic in appearance.