Why it matters: That's when it's especially important to limit time in the sun and cover up. UV radiation causes sunburn and is a risk factor for skin cancer. By the numbers: A UV index of 6-7 is ...

To help locate where a place is in the world, people use imaginary lines called latitude and longitude. Find out more with this year 3/4 BBC Bitesize geography guide.

THE photographic photometric methods used in the Utrecht Physical Laboratory were applied to some important lines of the infra-red solar spectrum. For the nearer infra-red at about 10000 A., the ...