snaangirl,
The BCP GPA enlists classes which contain Biology, Chemistry, and Physics course codes. There may be some variation on this from school to school. For instance, at my undergrad, Zoology 101 and 102 *are* biology classes, and so are included in the BCP GPA.
The science GPA includes any and all science classes, from astronomy to geology to food science, etc.
In regards to your question, the astronomy class would normally not be incorporated into your BCP GPA, but most certainly would count in your overall science GPA.