How do we see things?

Light from the sun, or an artificial  source, travels in a straight line and bounces off an object into the pupil (the pupil is a hole located in the centre of the iris that allows light to strike the retina) of the eye. Depending on the amount of light the iris (a flat, coloured, ring-shaped membrane behind the cornea of the eye, with an adjustable circular opening in the centre) changes the size of the pupil to let more or less light in. This is to prevent your eyes getting damaged, by stopping to much light entering the eye when it is bright, and maximising the amount of light entering the eye when it’s dark.