what does it mean to characterize a nebula as diffuse?

Question

a. it reflects only non-visible radiation
b. its edges do not have clear boundarious
c. its edges have clear boundaries
d. it reflects only visible radiation

Answer 1

To characterize a nebula as diffuse typically means that it does not have clear, well-defined edges. Therefore, the correct answer is:

b. its edges do not have clear boundaries.

Diffuse nebulae appear more spread out and lack the sharp outlines that are often seen in more compact or structured astronomical objects.