TIL - UV rise and sunrise are related but not the same.

Sunrise is when the sun first appears above the horizon, but at that moment the UV index is essentially zero (or very close to it). The sun’s rays are passing through a much thicker slice of atmosphere at such a low angle, which scatters and absorbs most of the UV radiation.

UV levels build gradually after sunrise and typically:
∙ Start becoming meaningful (UV index 1+) roughly 1–2 hours after sunrise
∙ Peak around solar noon (when the sun is highest in the sky), not at midday clock time
∙ Drop back to near zero 1–2 hours before sunset

A rough rule of thumb is that significant UV exposure happens in the middle portion of the day — often cited as 10am–4pm in summer at mid-latitudes like the UK.

Source: Claude