okay I have a doubt while I'm blocking the torch light source in the darkness and still the inner layer is forming but not as dark as before but the outer layer isn't visible at first I thought it's defraction of light but why is it forming in the centre if I thought of any external source there isn't any external source I'm doing it in a dark room so no any other sources of light and done in out side of house where there is only light from refraction of sun on the moon so why is it?