Answer:
It has a positive connotation, suggesting the astrophysicist’s long-lasting and innocent fascination with the universe.
Step-by-step explanation:
In the given sentence, the word "childlike" is used for an astrophysicist who was struck with awe and wonder when "looking at the stars in the night sky". This connotative use of the word "childlike" implies that he still retains that level of innocence and fascination he had during his childhood.
So, when looking at the way the sentence is framed/ constructed, we can see that it gives a positive sense of being. The word "retained" added with a "sense of wonder and never tired of looking at the stars in the night sky" all shows a positive impact of his childhood period, even in his adult life.
Thus, the best description for the usage of the word "childlike" is that it has a positive connotation in implying that he still retains his long lasting fascination with the universe.