Learn Portuguese (Portugal): Eu estudar o zodíaco e o mapa astral?! - Me study the zodiac and the astral chart?!

This is the Repudiation Infinitive (Infinitivo de repúdio). It is used in exclamatory questions to express shock, indignation, or total rejection of an idea. By pairing the subject directly with the infinitive, you are reacting to the very concept of the action: The idea of me studying the zodiac?! No way!

The English translation says 'Me study...?!'. Why does Portuguese use the subject pronoun eu instead of an object pronoun like mim?

In colloquial English, we often use object pronouns for this kind of exclamation ('Me do that?!', 'Him apologize?!'). However, in Portuguese, the verb still requires a valid grammatical subject, even in the infinitive form. Therefore, you must use the subject pronouns (eu, tu, ele, etc.). Saying mim estudar is grammatically impossible because mim can never perform an action.

If I wanted to express this same disbelief about 'us' doing it, would the verb change?

Yes, it would. The repudiation infinitive uses the personal infinitive, which means it still takes endings to match the subject. If you were shocked at the idea of 'us' studying the zodiac, you would say Nós estudarmos o zodíaco?!, adding the -mos ending to the infinitive to match nós.

Is a mapa astral just a map of the night sky?