Conversation so far:
Where did Matthew Fontaine Maury grow up?
He was born in 1806 in Spotsylvania County, Virginia, near Fredericksburg.
Did they stay there?
The family moved to Franklin, Tennessee, when he was five.
How or when did he become interested in astronomy or the ocean?
He wanted to emulate the naval career of his older brother, Flag Lieutenant John Minor Maury.

Question: What made him interested in astronomy?
Self-contained rewrite: What made Matthew Fontaine Maury interested in astronomy?