Why are the sun’s UV rays more harmful in the afternoon than in the morning or evening?

Question

I always hear that we should avoid the sun or make sure to put on sunscreen in the afternoon when the sun is the most intense. Why is the sun’s rays more harmful when it is directly overhead vs in the morning soon after sunrise? Either way, the sun is shining directly on me so not sure what causes the difference in intensity.

In: Planetary Science

Answer 1

Theirs less air between you and the sun at noon.

Directly overhead there is 1 airmass of air above you

If you deviate from the zenith, now light from something over there takes a longer path through the atmosphere to reach you.

This peaks at 38 airmasses at the horizon, meaning at sunrise and sunset, the sunlight passes through 38x more air to reach you than if it were directly overhead.