I have been told that the longer you stare at the night sky, slowly more stars will appear and become visible. I have tried this by letting my eyes get adjusted to the dark first and then staring at the night sky for hours on end, and it seems to be true, the longer you stare the more stars seem to appear. Why is that so? Is it that the light from stars are just reaching Earth making stars seem to appear or is it your eyes noticing dimly lit stars?