Stargazers know that faint objects in the night sky become more visible when you don’t stare directly at them. Why is it that when you look at a faint star, it’s brighter when you’re looking away from it than when you’re looking directly at it?
The reason stars look brighter when you look away from them has to do with the structure of your eyes. At the back of your eye, there’s a light-sensitive layer known as the retina. The retina has two different kinds of light-sensitive cells — cones and rods — which are named for their shapes.
Cone cells are involved in sharp, color vision. Rod cells, on the other hand, are more sensitive to light and dark. You have more cone cells in the center of your retina. But at the sides, you have more rods. This is probably because peripheral vision evolved as a warning of things about to happen. So creatures with more sensitive vision at the sides must have had an advantage.
Since you have more rod cells off to the sides of your retina, your vision’s more sensitive there — but it’s not as sharp as if you were looking at something straight on. That’s why faint objects in the sky might disappear when you stare at them, but reappear when you turn away.