The UV index is a measure of how strong the sun's ultraviolet (UV) radiation is at a particular time and location. It is expressed as a number from 0 to 11+, with higher numbers indicating a greater risk of skin damage and sunburn.

The UV index is calculated by taking into account several factors, including:

* The position of the sun in the sky. The closer the sun is to the zenith (the point directly overhead), the higher the UV index.

* The time of day. The UV index is typically highest in the middle of the day, when the sun is at its highest point in the sky.

* The amount of ozone in the atmosphere. Ozone absorbs UV radiation, so the more ozone there is in the atmosphere, the lower the UV index.

* The presence of clouds. Clouds can block UV radiation, so the cloudier it is, the lower the UV index.

The UV index is a helpful tool for planning outdoor activities and protecting your skin from sun damage. It is recommended that you limit your exposure to the sun when the UV index is 6 or higher and that you take precautions to protect your skin, such as wearing sunscreen, sunglasses, and a hat.

You can find the UV index for your location by checking the weather forecast or by using a UV index app.