When there is still sunlight at 5pm, and the temperature is just as hot as it is at 1pm, why is the UV index significantly lower in the evening?
In: Planetary Science
The UV index is mostly affected by how much and what type of atmosphere the sunlight goes through. It’s why higher altitudes get more, for example; the higher altitude means there’s less atmosphere, which means more sunlight makes it through.
Now, what happens when you take a straw that is straight up in a glass, but then lean it diagonally across the cup? Suddenly, the straw is going through more water.
Similarly, if you take the sunlight that is mostly vertical at noon but then have it more diagonal in the evening, it is suddenly going through more atmosphere than before. Therefore, the UV index will be lower in the evening than when the sun is the highest.
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