The sun produces different types of radiation, visible light (that we see as sunlight), infrared radiation (we feel as heat) and ultraviolet (UV) radiation that can't be seen or felt. People often confuse visible light, and infrared radiation with UV radiation. In fact, even when the temperature is cool it doesn't necessarily mean less UV radiation.

The three types of UV radiation are:
- UVA (most common) which doesn't cause sunburn, but can cause longer term DNA (cell) damage, and skin cancer.
- UVB which causes sunburn, DNA damage and skin cancer, but provides us with important Vitamin D. Ozone stops most UVB from reaching the earth's surface.
- UVC which is the most dangerous type of UV and is completely absorbed by the Ozone layer so that none reaches the earth's surface.

UV levels vary depending on factors such as the time of day, time of year, latitude, cloud cover, ozone cover, and reflection from surfaces. When the UV index is greater than or equal to 3, sun protection is recommended.

WillyWeather sources its UV information from the National Oceanic and Atmospheric Administration. The NOAA is the US Government agency that forecasts global weather, similar to the Bureau of Meteorology but many times larger. UV forecasts are updated every 24 hours. To see when the last UV forecast was issued and when the next UV forecast will be issued, please see the text beneath the graph.