Any idea how deep the eye could go if there was no atmosphere to scatter starlight? Ever wonder what optical and physical principles limit the eye’s ability to see small, faint things? Have you given thought to how the “why” of astronomy changed before and after the telescope? In this article Jeff Barbour explores the limits of human sight – with and without the telescope. Learn more about the equipment available to contemporary amateurs making backyard astronomy the “extra-terrestrial” hobby of choice.