UV Index:

A measure of the intensity of ultraviolet (UV) radiation received at the Earth's surface, the UV index indicates how safe it is to be outside in the sun. Too much exposure to UV radiation can cause sunburn and may lead to skin cancer, cataracts and other health problems with repeated long periods in the sun.

UV scale

Green (0-2) indicates low danger: use SPF30+ sunscreen

Yellow (3-5) indicates moderate risk of harm: apply SPF30+ sunscreen every 2 hours

Orange (6-7) indicates high risk: apply SPF30+ sunscreen every 2 hours and reduce exposure between 10am-4pm

Red (8-10) indicates very high risk: apply SPF30+ sunscreen every 2 hours and minimize exposure between 10am-4pm

Purple (11+) indicates extreme risk: avoid the sun between 10am-4pm

NOAA's National Weather Service forecasts the UV Index using a computer model that relates incoming sunlight at different ultraviolet wavelenths (280-400nm) to the sun's angle (determined by latitude, day of the year and time of day), ozone layer thickness, clouds, amount of air pollution, land elevation and the sensitivity of human skin to UV radiation.


Current UV Index forecast by the National Weather Service

UV impacts avoided by the Montreal Protocol

EPA UV Index

Strongest UV rays ever measured on Earth

Dataset Information:

NASA Earth Observations UV Index

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