This is how I burned my retina. I was watching the sun go down at sea waiting for a 'green flash' which is shown in the image. I guess I looked at the setting sun too long and it made a black spot on my retinas. Eventually the black spot went away, but it took many years before it cleared up.
A green flash occurs at sea at sunrise or sunset. When the sun dips below the horizon in some places on the ocean, the sun will shine through the water from the other side of the world to your horizon. This creates a green flash (called a flash because it only lasts for a second) on the horizon where the sun is. I have only seen this in person one time. I was very lucky because the green flash phenomenon is very rare.
