Final answer:
The term "astronomical" in the context given most likely means extremely large, reflecting the vast scales in astronomy.
The correct option is D.
Step-by-step explanation:
The word "astronomical" most likely means extremely large as used in paragraph 3 of the provided context. This meaning is evident because the paragraph and surrounding content often discuss measurements, distances, and sizes that are beyond typical human comprehension, such as the distances to stars, the mass of the Milky Way Galaxy, and the discovery of planets in astronomical research.
It does not imply weight or incredulity, nor does it directly refer to stars in this context, although "astronomical" can be related to stars in other contexts.
The correct option is D.