Final answer:
The appositive phrase in the sentence is 'an astronaut,' which provides additional information about the noun 'father.'
Step-by-step explanation:
In the sentence provided, the appositive phrase is 'an astronaut,' which renames or identifies the noun 'father.' An appositive is a noun or noun phrase that follows another noun immediately and defines or amplifies its meaning.
It is usually set off by commas. In this instance, the appositive provides additional information about the student's father's occupation.