The inquiry seeks the designation for an individual engaged in the study of celestial bodies. The provided options are evaluated as follows:
Biologist: Specializes in the scientific study of life. This is irrelevant to the subject matter.
Geologist: Focuses on the study of the Earth's physical structure and substance. This is also unrelated to the query.
Astronomer: A scientist dedicated to the study of celestial objects, including stars and planets. This precisely matches the query's requirement.
Physicist: Studies matter, energy, and the fundamental laws of the universe. While overlapping with astronomical phenomena, 'Astronomer' is the more specific and accurate term.
Consequently, the accurate classification is: Astronomer.