EVER rubbed your eyes vigorously and you'll probably have witnessed an explosion of stars.
If you've wondered how you can see this fantastical swirl of patterns and colour without even opening your eyes, science has an answer.
The shapes and colours you see have been a recognised phenomenon since the time of the ancient Greeks.
The word phosphene describes the experience of seeing light without light actually entering your eyes.
Increased pressure on the eyeballs - caused by rubbing, for example - activates ganglion cells in the retina, fooling your brain into thinking you were seeing light from the outside.
These are known as pressure phosphenes, and include a darkening of the visual field, a coloured patch and an ever-changing grid of light with the odd dark spot.
This article originally appeared on The Sun and has been republished with permission.