The correct answer is the third option "It has a positive connotation, suggesting the astrophysicist’s long-lasting and innocent fascination with the universe."
The use of words like "sense of wonder" and " looking at the night sky" are adding meaning, specifically an explanation to the word "childlike", have a positive meaning. Thus, the author wants to emphasize that the asthrophysicist never lost his original curiosity and fascination for the study of the stars, so the word "childlike" refers to his passion being quite similar to that of a child.