Learn Italian: Lo scrittore dell'opera viaggiava quando è nato suo figlio. - The writer of the work was traveling when his son was born.

This is a perfect example of how these two past tenses work together! Viaggiava (was traveling) is in the imperfetto because it describes an ongoing background action. È nato (was born) is in the passato prossimo because it is a specific, single event that interrupted or happened during that ongoing travel.

Why is the auxiliary verb è used in è nato instead of ha?

The verb for "to be born" is nascere, and its irregular past participle is nato. Because being born describes a profound change of state (coming into existence), it requires the auxiliary verb essere (to be) to form the passato prossimo.

I remember that possessives usually need an article like "il" or "la". Why is it just suo figlio and not il suo figlio?

You remembered the general rule! However, there is a strict exception for family members in Italian. When talking about a singular, unmodified family member like figlio (son), you must drop the definite article. If it were plural, the article would come back, as in i suoi figli (his sons).

How does the word dell'opera break down?