Why doesn’t it hurt to look at the sun during a sunrise/sunset? — Jesus, Kissimmee, Florida
It is never a good idea to look directly at the sun. But at sunrise and sunset, when the sun is only halfway above the horizon and has that reddish color, many people look at it anyway. To understand why they can do this, think about the thickness of the atmosphere. At noon on a summer day, the sun is directly overhead. It has to punch through 60 miles of vertical “atmosphere” to get to the ground. Keep in mind that the atmosphere gets thicker and thicker as you get closer to the ground, and the last mile or so closest to the ground is the thickest.
When you are looking at a sunset, the sunlight is coming at you horizontally rather than vertically. It has traveled many miles through the thickest layer of the atmosphere to reach your eyes, plus the many more miles of thin atmosphere above that. All that atmosphere blocks a huge amount of the light before it gets to your eyes and gives the sun its red color. Therefore, the sunlight is very dim compared to the sunlight at noon, and does little damage to your eyes.
See also: What happens when we stare at the sun?