The astronomer has to choose 3 star images out of 8.This is a problem of combinations. This can be expressed as 8C3 i.e. combination of 8 objects taken 3 at a time.
This means, if 8 images are nearby the astronomer will have 56 choices <span>of the three stars.</span>
This means, if 8 images are nearby the astronomer will have 56 choices <span>of the three stars.</span>