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There are four seasons in the year in the UK, but what causes them and how do they affect us?
Tree pollen occurs first, typically from late March to mid-May. Grass (which actually has two peaks) lasts from mid-May until July, and weed pollen covers the end of June to September.
The sky appears blue to the human eye as the short waves of blue light are scattered more than the other colours in the spectrum, making the blue light more visible.
Find out more about ultraviolet (UV) radiation from the sun and its positive and negative effects on our health.
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