*Afterimages*
An afterimage is an image that continues to appear in the eyes after a period of exposure to the original image. An afterimage may be a normal phenomenon (physiological afterimage) or may be pathological (palinopsia). Afterimages occur because in the retina of your eyes, there are 3 types of color receptors (cones) that are most sensitive to either red, blue or green. When you stare at a particular colour for too long, these receptors get "tired" or "fatigued." When you then look at the white background, the receptors that are tired do not work as well. Therefore, the information from all of the different colour receptors is not in balance and you see the colour "afterimages." After a short period of time, you vision returns to normal.
*To get the afterimage look at the picture above, and look closely at the tiny white dot between the eyes. You need to stare ONLY at this tiny white dot, while counting slowly to 30. don’t look away at all, and try not to even blink. At the count of 30, then look up at the sky and blink quickly. You will see the afterimage. This works even better if it is overcast. look at the sky with the sun behind you. what do you see?*
*Here's another one*
*Stare at the top dot in the image above To get the afterimage look at the picture above, and stare at the top dot in the image above. You need to stare ONLY at this tiny top black dot, while counting slowly to 30. Don’t look away at all, and try not to even blink. At the count of 30, then look up at the sky and blink quickly. You will see the afterimage. This works even better if it is overcast. Only look at the sky with the sun behind you. What do you see?*
*Here is an interesting one:*
*Stare at the small cross in the middle, and watch the gap in the ring of purple dots turn to Green, and keep watching, and all the purple dots will disappear, leaving only the green dot going round.*
