In this activity about light and perception, learners discover how a flash of light can create a lingering image called an "afterimage" on the retina of the eye. Learners will be surprised when they continue to see an image of a bright object after staring at it and looking away. Use this activity to introduce learners to principles of optics and perception as well as to explain why the full moon often appears larger when it is on the horizon than when it is overhead. This lesson guide also includes a few extensions like how to take "afterimage photographs."