What makes a nebula planetary and what makes a nebula diffuse? Is there any way to tell if they are Diffuse or Planetary just by looking at a picture? What are some Diffuse Nebulae? What are some Planetary Nebulae?

Question

What makes a nebula planetary and what makes a nebula diffuse?  Is there any way to tell if they are Diffuse or Planetary just by looking at a picture?  What are some Diffuse Nebulae?  What are some Planetary Nebulae?

Josiah Adams · Accepted Answer

Planetary nebulae are round and tend to have distinct edges, diffuse nebulae are spread out, randomly shaped, and tend to fade away at the edges.

Despite the name, planetary nebulae have noting to do with planets. They are the cast-off outer layers of a dying star. Those outer layers spread out uniformly in a bubble, so they tend to appear circular in a telescope. This is where the name comes from - in a telescope they look round the way planets appear, so "planetary" describes the shape, not what they do.

The gasses are made to glow by ultra-violet radiation emitted by the white dwarf that is all that remains of the original star.

Classic examples are the ring nebula (M57):

Owen Atkinson · Answer

undefined Diffuse nebulae are clouds of gas and dust where new stars are forming, whereas planetary nebulae are formed from the outer layers of stars that have reached the end of their life cycle. Diffuse nebulae appear more spread out and lack distinct boundaries, whereas planetary nebulae are formed from the outer layers of stars that have reached the end of their life cycle. Images can be used to distinguish between diffuse and planetary nebulae. Examples of diffuse nebulae are the Orion Nebula and the Lagoon Nebula, whereas planetary nebulae are formed from the ends of stars.