Use the coloured baseboard on the first page as your starting point. As your class reads the shortlisted books or you complete activities related to the books, place one of these planets onto your base picture.
Keep going until all of the planets are filled in.
I recommend that you enlarge both the baseboard and the planets to A3, then laminate the pages (before cutting out the planets) to ensure durability during the event.
OPTION 2: Print off one black and white page per student (page 2) as A4, then as an activity is completed / book is read, each student colours in a planet.