I learned in school that seasonality is due to the earth’s tilt. Summer (in which hemisphere you live in) is hot because the sun shines on your part of the earth for more hours than it does in winter. Makes sense, but how does the UV Index work? I’ve been checking it recently and a hour of sunshine at this time of the year is much more damaging than other times. IDK if it’s in my mind but sunshine on my skin just feels… “burnier.” Presumably the amount of radiation the sun puts out doesn’t vary with seasons. It is also due to angle? Is it something with heat? Am I imagining this?
In: Planetary Science
>It is also due to angle?
You guessed it.
The higher the Sun is in the sky, the less sky (aka. atmosphere) the light needs to pass through to reach you. Since part of the atmosphere is made partly of ozone (which strongly absorbs UV), passing through less of it before hitting the surface means a lot more UV reaches you.
Edit to add: this is also why angle isn’t the only factor in calculating the UV index. Different parts of the atmosphere contain more or less ozone, and of course, things like clouds will flat out reflect a bunch of light (of all wavelengths).
>Is it something with heat? Am I imagining this?
The “burnier” feel is indeed mostly due to heat. The visible and infrared portions of sunlight carry far more energy than the UV portion, and the longer wavelengths in particular penetrate deeper into your skin.
>Presumably the amount of radiation the sun puts out doesn’t vary with seasons.
While true, the distance to the Sun does vary with season, but in the opposite direction of what you’d expect (living in the northern hemisphere).
We’re currently getting further and further away from the Sun, with the greatest distance (and as a result, least total radiation hitting Earth) being reached in early July.
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