In the late 1600s, Isaac Newton conducted a series of experiments that broke the two most fundamental rules of eye safety — in one, he stared at the sun, and in the other, he stuck a needle under his eyeball.
Newton was hoping to better understand the lights and colors that sometimes appear when your eyes are closed.
If you've ever sat around an evening campfire or, unlike Newton, unintentionally glanced at the sun, you may have noticed illuminated patterns briefly dance along your vision before fading into darkness.
So how do these visual illusions, known as afterimages, form?
Inside the retina, specialized cells called photoreceptors take in light and turn it into a signal the brain can understand.
Photoreceptors contain thousands of molecules called photopigments, which are sensitive to particular colors.
When a light-photon strikes a pigment, part of the photopigment's structure, known as chromophore, absorbs the energy by temporarily altering its molecular structure in a process called bleaching.
This reconfiguration induces a cascade of chemical reactions that route an electrical pulse to the brain.
And once your brain assembles the signals from approximately 200 million photoreceptor cells, you see an image.
So how does this lead to an afterimage?
