Stare at the blue dots
Stare at the blue dots while you count slowly to 30.
Then close your eyes and tilt your head back. A circle of light will slowly appear. Keep looking at it. What do you see?
Try this again, but look at a white wall after 30 seconds. Do you still see it?
Most people see an ‘apparition’ of a man – perhaps Jesus.
When you look at a white wall, the image appears much bigger.
Staring at the bright white areas of the picture tires out some of the light-sensitive detectors in your retina (at the back of your eye).
When you then closed your eyes - or looked at a white wall - you see a negative after-image.
The areas that were white now look black.
Mars is home to the largest known volcano in the Solar System, Olympus Mons